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*Sketch of the Analytical Engine invented by*Charles Babbage, Esq.*By*L. F. MENABREA,

*of Turin, Officer of the Military Engineers.**Bibliothèque Universelle de Genève*, No. 82

Translation orignally published in 1843 in the *Scientific Memoirs*, *3*, 666-731.

*[*Classics

*Editor's note: The following document has a rather complicated publication history. In August of 1840 Charles Babbage gave a series of lecturs on his Analytical Engine in Turin. Luigi Menabrea--then an obscure military engineer, but later to become a general in Garibaldi's army and prime minister of Italy--published an account of Babbage's lectures in French in the*Bibliothèque Universelle de Genève

*in October of 1842. In early 1843 this article was translated into English by Augusta Ada Byron King, Countess of Lovelace, who then added extensive "Notes" written in close collaboration with Babbage. The translation and Notes were published in Richard Taylor's*Scientific Memoirs

*in October 1843, and were preceded by a short account of Babbage's exploits written by Taylor himself (viz., the initial portion of the document in square brackets and signed "Editor"). Lovelace left the translation anonymous (as was customary at the time) but signed the Notes "A.A.L." so that readers would know that they were written by the same person as future works of hers to be identified in the same way. As it turned out, however, she would publish no other scholarly work. Since its original publication, the article and Notes have been republished several times, with various "corrections" and changes. The complete piece was republished by H.P. Babbage in 1889 as part of a collection entitled*Babbage's Calculating Engines

*. The following document is based on that edition. It was also republished in B.V. Bowden's*Faster than Thought

*in 1953, and in P. & E. Morrison's*Charles Babbage and his Calculating Engines

*in 1961. The key differences between these texts are discussed in the footnotes included in the version below. CDG]*

[Before submitting to our readers the translation of M. Menabrea's memoir 'On the Mathematical Principles of the ANALYTICAL ENGINE' invented by Mr. Babbage, we shall present to them a list of the printed papers connected with the subject, and also of those relating to the Difference Engine by which it was preceded.

For information on Mr. Babbage's "*Difference *Engine," which is
but slightly alluded to by M. Menabrea, we refer the reader to the following
sources:-

1. Letter to Sir Humphry Davy, Bart., P.R.S., on the Application of Machinery to Calculate and Print Mathematical Tables. By Charles Babbage, Esq., F.R.S. London, July 1822. Reprinted, with a Report of the Council of the Royal Society, by order of the House of Commons, May 1823.

2. On the Application of Machinery to the Calculation of Astronomical and Mathematical Tables. By Charles Babbage, Esq. - Memoirs of the Astronomical Society, vol. i. part 2. London, 1822.

3. Address to the Astronomical Society by Henry Thomas Colebrooke, Esq., F.R.S., President, on presenting the first Gold Medal of the Society to Charles Babbage, Esq., for the invention of the Calculating Engine.- Memoirs of the Astronomical Society. London, 1822.

4. On the Determination of the General Term of a New Class of Infinite Series. By Charles Babbage, Esq.- Transactions of the Cambridge Philosophical Society.

5. On Mr. Babbage's New Machine for Calculating and Printing Mathematical Tables.- Letter from Francis Baily, Esq., F.R.S., to M. Schumacher. No. 46, Astronomische Nachrichten. Reprinted in the Philosophical Magazine, May 1824.

6. On a Method of expressing by Signs the Action of Machinery. By Charles Babbage, Esq.- Philosophical Transactions. London, 1826.

7. On Errors common to many Tables of Logarithms. By Charles Babbage, Esq.- Memoirs of the Astronomical Society. London, 1827.

8. Report of the Committee appointed by the Council of the Royal Society to consider the subject referred to in a communication received by them from the Treasury respecting Mr. Babbage's Calculating Engine, and to report thereon. London, 1829.

9. Economy of Manufactures, chap. xx. 8vo. London, 1832.

10. Article on Babbage's Calculating Engine,- Edinburgh Review, July 1834. No. 120. vol. lix.

The present state of the Difference Engine, which has always been the property of Government, is as follows:- The drawings are nearly finished, and the mechanical notation of the whole, recording every motion of which it is susceptible, is completed. A part of the Engine, comprising sixteen figures, arranged in three orders of differences, has been put together, and has frequently been used during the last eight years. It performs its work with absolute precision. This portion of the Difference Engine, together with all the drawings, are at present deposited in the Museum of King's College, London.

Of the ANALYTICAL ENGINE*, *which forms the
principal object of the present memoir, we are not aware that any notice
has hitherto appeared, except a Letter from the Inventor to M. Quetelet,
Secretary to the Royal Academy of Sciences at Brussels, by whom it was
communicated to that body. We subjoin a translation of this Letter, which
was itself a translation of the original, and was not intended for publication
by its author.

*Royal Academy of Sciences at Brussels. General Meeting of the 7th and 8th of May,*1835

*.*

"A Letter from Mr. Babbage announces that he has for six months been engaged in making the drawings of a new calculating machine of far greater power than the first.

"I am myself astonished,' says Mr. Babbage, 'at the power I have been
enabled to give to this machine; a year ago I should not have believed
this result possible. This machine is intended to contain a hundred variables
(or numbers susceptible of changing); each of these numbers may consist
of twenty-five figures, *v*_{1}, *v*_{2}, . .
. . . *v _{n}* being any numbers whatever,

*n*being less than a hundred; if

*f*(

*v*

_{1},

*v*

_{2},

*v*

_{3}, . .

*v*) be any given function which can be formed by addition, subtraction, multiplication, division, extraction of roots, or elevation to powers, the machine will calculate its numerical value; it will afterwards substitute this value in the place of

_{n}*v*, or of any other variable, and will calculate this second function with respect to

*v*. It will reduce to tables almost all equations of finite differences. Let us suppose that we have observed a thousand values of

*a*,

*b*,

*c*,

*d*, and that we wish to calculate them by the formula

*p*= SqR [(a+b) / (cd)], the machine must be set to calculate the formula; the first series of the values of

*a*,

*b*,

*c*,

*d*must be adjusted to it; it will then calculate them, print them, and reduce them to zero; lastly, it will ring a bell to give notice that a new set of constants must be inserted. When there exists a relation between any number of successive coefficients of a series, provided it can be expressed as has already been said, the machine will calculate them and make their terms known in succession; and it may afterwards be disposed so as to find the value of the series for all the values of the variable.'

"Mr. Babbage announces, in conclusion,' that the greatest difficulties of the invention have already been surmounted, and that the plans will be finished in a few months.'"

In the Ninth Bridgewater Treatise, Mr. Babbage has employed several arguments deduced from the Analytical Engine, which afford some idea of its powers. See Ninth Bridgewater Treatise, 8vo, second edition. London, 1834.

Some of the numerous drawings of the Analytical Engine have been engraved on wooden blocks, and from these (by a mode contrived by Mr. Babbage) various stereotype plates have been taken. They comprise -

1. Plan of the figure wheels for one method of adding numbers.

2. Elevation of the wheels and axis of ditto.

3. Elevation of framing only of ditto.

4. Section of adding wheels and framing together.

5. Section of the adding wheels, sign wheels and framing complete.

6. Impression from the original wooden block.

7. Impressions from a stereotype cast of No. 6, with the letters and
signs inserted. Nos. 2, 3, 4 and 5 were stereotypes taken from this.

8. Plan of adding wheels and of long and short pinions, by means of
which *stepping* is accomplished.

N.B. This process performs the operation of multiplying or dividing
a number by any power of ten.

9. Elevation of long pinions in the position for addition.

10. Elevation of long pinions in the position for stepping.

11. Plan of mechanism for carrying the tens (by anticipation), connected
with long pinions.

12. Section of the chain of wires for anticipating carriage.

13. Sections of the elevation of parts of the preceding carriage.

All these were executed about five years ago. At a later period (August 1840) Mr. Babbage caused one of his general plans (No. 25) of the whole Analytical Engine to be lithographed at Paris.

Although these illustrations have not been published, on account of the time which would be required to describe them, and the rapid succession of improvements made subsequently, yet copies have been freely given to many of Mr. Babbage's friends, and were in August 1838 presented at Newcastle to the British Association for the Advancement of Science, and in August 1840 to the Institute of France through M. Arago, as well as to the Royal Academy of Turin through M. Plana. - EDITOR.]

*Sketch of the Analytical Engine invented by*Charles Babbage,*Esq*.*By*. L. F. MENABREA,

*of Turin, Officer of the Military Engineers.**Bibliothèque Universelle de Genève*, No. 82. October 1842.]

*correctness*in the results, united with

*economy*of time.

Struck with similar reflections, Mr. Babbage has devoted some years to the realization of a gigantic idea. He proposed to himself nothing less than the construction of a machine capable of executing not merely arithmetical calculations, but even all those of analysis, if their laws are known. The imagination is at first astounded at the idea of such an undertaking; but the more calm reflection we bestow on it, the less impossible does success appear, and it is felt that it may depend on the discovery of some principle so general, that, if applied to machinery, the latter may be capable of mechanically translating the operation which may be indicated to it by algebraical notation. The illustrious inventor having been kind enough to communicate to me some of his views on this subject during a visit he made at Turin, I have, with his approbation, thrown together the impressions they have left on my mind. But the reader must not expect to find a description of Mr. Babbage's engine; the comprehension of this would entail studies of much length; and I shall endeavour merely to give an insight into the end proposed, and to develope the principles on which its attainment depends.

I must first premise that this engine is entirely different from that of which there is a notice in the 'Treatise on the Economy of Machinery,' by the same author. But as the latter gave rise[2] to the idea of the engine in question, I consider it will be a useful preliminary briefly to recall what were Mr. Babbage's first essays, and also the circumstances in which they originated.

It is well known that the French government, wishing to promote the extension of the decimal system, had ordered the construction of logarithmical and trigonometrical tables of enormous extent. M. de Prony, who had been entrusted with the direction of this undertaking, divided it into three sections, to each of which was appointed a special class of persons. In the first section the formulae were so combined as to render them subservient to the purposes of numerical calculation; in the second, these same formulae were calculated for values of the variable, selected at certain successive distances; and under the third section, comprising about eighty individuals, who were most of them only acquainted with the first two rules of arithmetic, the values which were intermediate to those calculated by the second section were interpolated by means of simple additions and subtractions.

An undertaking similar to that just mentioned having been entered upon in England, Mr. Babbage conceived that the operations performed under the third section might be executed by a machine; and this idea he realized by means of mechanism, which has been in part put together, and to which the name Difference Engine is applicable, on account of the principle upon which its construction is founded. To give some notion of this, it will suffice to consider the series of whole square numbers, 1, 4, 9, 16, 25, 36, 49, 64, &c. By subtracting each of these from the succeeding one, we obtain a new series, which we will name the Series of First Differences, consisting of the numbers 3, 5, 7, 9, 11, 13, 15, &c. On subtracting from each of these the preceding one, we obtain the Second Differences, which are all constant and equal to 2. We may represent this succession of operations, and their results, in the following table: -

*a b*. Similarly, we obtain the number 25 by summing up the three numbers placed in the oblique direction

*d c*: commencing by the addition 2 + 7, we have the first difference 9 consecutively to 7; adding 16 to the 9 we have the square 25. We see then that the three numbers 2, 5, 9 being given, the whole series of successive square numbers, and that of their first differences likewise, may be obtained by means of simple additions.

Now, to conceive how these operations may be reproduced by a machine, suppose the latter to have three dials, designated as A, B, C, on each of which are traced, say a thousand divisions, by way of example, over which a needle shall pass. The two dials, C, B, shall have in addition a registering hammer, which is to give a number of strokes equal to that of the divisions indicated by the needle. For each stroke of the registering hammer of the dial C, the needle B shall advance one division; similarly, the needle A shall advance one division for every stroke of the registering hammer of the dial B. Such is the general disposition of the mechanism.

This being understood, let us, at the beginning of the series of operations we wish to execute, place the needle C on the division 2, the needle B on the division 5, and the needle A on the division 9. Let us allow the hammer of the dial C to strike; it will strike twice, and at the same time the needle B will pass over two divisions. The latter will then indicate the number 7, which succeeds the number 5 in the column of first differences. If we now permit the hammer of the dial B to strike in its turn, it will strike seven times, during which the needle A will advance seven divisions; these added to the nine already marked by it will give the number 16, which is the square number consecutive to 9. If we now recommence these operations, beginning with the needle C, which is always to be left on the division 2, we shall perceive that by repeating them indefinitely, we may successively reproduce the series of whole square numbers by means of a very simple mechanism.

The theorem on which is based the construction of the machine we have
just been describing, is a particular case of the following more general
theorem: that if in any polynomial whatever, the highest power of whose
variable is *m*, this same variable be increased by equal degrees;
the corresponding values of the polynomial then calculated, and the first,
second, third, &c. differences of these be taken (as for the preceding
series of squares); the *m*th differences will all be equal to each
other. So that, in order to reproduce the series of values of the polynomial
by means of a machine analogous to the one above described, it is sufficient
that there be (*m *+ 1) dials, having the mutual relations we have
indicated. As the differences may be either positive or negative, the machine
will have a contrivance for either advancing or retrograding each needle,
according as the number to be algebraically added may have the sign *plus
*or *minus*.

If from a polynomial we pass to a series having an infinite number of terms, arranged according to the ascending powers of the variable, it would at first appear, that in order to apply the machine to the calculation of the function represented by such a series, the mechanism must include an infinite number of dials, which would in fact render the thing impossible. But in many cases the difficulty will disappear, if we observe that for a great number of functions the series which represent them may be rendered convergent; so that, according to the degree of approximation desired, we may limit ourselves to the calculation of a certain number of terms of the series, neglecting the rest. By this method the question is reduced to the primitive case of a finite polynomial. It is thus that we can calculate the succession of the logarithms of numbers. But since, in this particular instance, the terms which had been originally neglected receive increments in a ratio so continually increasing for equal increments of the variable, that the degree of approximation required would ultimately be affected, it is necessary, at certain intervals, to calculate the value of the function by different methods, and then respectively to use the results thus obtained, as data whence to deduce, by means of the machine, the other intermediate values. We see that the machine here performs the office of the third section of calculators mentioned in describing the tables computed by order of the French government, and that the end originally proposed is thus fulfilled by it.

Such is the nature of the first machine which Mr. Babbage conceived.
We see that its use is confined to cases where the numbers required are
such as can be obtained by means of simple additions or subtractions; that
the machine is, so to speak, merely the expression of one[3]
particular theorem of analysis; and that, in short, its operations cannot
be extended so as to embrace the solution of an infinity of other questions
included within the domain of mathematical analysis. It was while contemplating
the vast field which yet remained to be traversed, that Mr. Babbage, renouncing
his original essays, conceived the plan of another system of mechanism
whose operations should themselves possess all the generality of algebraical
notation, and which, on this account, he denominates the *Analytical
Engine*.

Having now explained the state of the question, it is time for me to
develope the principle on which is based the construction of this latter
machine. When analysis is employed for the solution of any problem, there
are usually two classes of operations to execute: first, the numerical
calculation of the various coefficients; and secondly, their distribution
in relation to the quantities affected by them. If, for example, we have
to obtain the product of two binomials (*a *+ *bx*) (*m *+
*nx*), the result will be represented by *am *+ (*an *+
*bm*) *x *+ *bnx ^{2}*, in which expression we must
first calculate

*am*,

*an*,

*bm*,

*bn*; then take the sum of

*an*+

*bm*; and lastly, respectively distribute the coefficients thus obtained amongst the powers of the variable. In order to reproduce these operations by means of a machine, the latter must therefore possess two distinct sets of powers: first, that of executing numerical calculations; secondly, that of rightly distributing the values so obtained.

But if human intervention were necessary for directing each of these
partial operations, nothing would be gained under the heads of correctness
and economy of time; the machine must therefore have the additional requisite
of executing by itself all the successive operations required for the solution
of a problem proposed to it, when once the *primitive numerical data
*for this same problem have been introduced. Therefore, since, from
the moment that the nature of the calculation to be executed or of the
problem to be resolved have been indicated to it, the machine is, by its
own intrinsic power, of itself to go through all the intermediate operations
which lead to the proposed result, it must exclude all methods of trial
and guess-work, and can only admit the direct processes of calculation[4].

It is necessarily thus; for the machine is not a thinking being, but simply an automaton which acts according to the laws imposed upon it. This being fundamental, one of the earliest researches its author had to undertake, was that of finding means for effecting the division of one number by another without using the method of guessing indicated by the usual rules of arithmetic. The difficulties of effecting this combination were far from being among the least; but upon it depended the success of every other. Under the impossibility of my here explaining the process through which this end is attained, we must limit ourselves to admitting that the first four operations of arithmetic, that is addition, subtraction, multiplication and division, can be performed in a direct manner through the intervention of the machine. This granted, the machine is thence capable of performing every species of numerical calculation, for all such calculations ultimately resolve themselves into the four operations we have just named. To conceive how the machine can now go through its functions according to the laws laid down, we will begin by giving an idea of the manner in which it materially represents numbers.

Let us conceive a pile or vertical column consisting of an indefinite
number of circular discs, all pierced through their centres by a common
axis, around which each of them can take an independent rotatory movement.
If round the edge of each of these discs are written the ten figures which
constitute our numerical alphabet, we may then, by arranging a series of
these figures in the same vertical line, express in this manner any number
whatever. It is sufficient for this purpose that the first disc represent
units, the second tens, the third hundreds, and so on. When two numbers
have been thus written on two distinct columns, we may propose to combine
them arithmetically with each other, and to obtain the result on a third
column. In general, if we have a series of columns[5]
consisting of discs, which columns we will designate as V_{0},
V_{1}, V_{2}, V_{3}, V_{4}, &c., we
may require, for instance, to divide the number written on the column V_{1}
by that on the column V_{4}, and to obtain the result on the column
V_{7}. To effect this operation, we must impart to the machine
two distinct arrangements; through the first it is prepared for executing
*a division*, and through the second the columns it is to operate
on are indicated to it, and also the column on which the result is to be
represented. If this division is to be followed, for example, by the addition
of two numbers taken on other columns, the two original arrangements of
the machine must be simultaneously altered. If, on the contrary, a series
of operations of the same nature is to be gone through, then the first
of the original arrangements will remain, and the second alone must be
altered. Therefore, the arrangements that may be communicated to the various
parts of the machine may be distinguished into two principal classes:

First, that relative to the *Operations*.

Secondly, that relative to the *Variables*.

By this latter we mean that which indicates the columns to be operated
on. As for the operations themselves, they are executed by a special apparatus,
which is designated by the name of *mill*, and which itself contains
a certain number of columns, similar to those of the Variables. When two
numbers are to be combined together, the machine commences by effacing
them from the columns where they are written, that is, it places *zero*[6]*
*on every disc of the two vertical lines on which the numbers were represented;
and it transfers the numbers to the mill. There, the apparatus having been
disposed suitably for the required operation, this latter is effected,
and, when completed, the result itself is transferred to the column of
Variables which shall have been indicated. Thus the mill is that portion
of the machine which works, and the columns of Variables constitute that
where the results are represented and arranged. After the preceding explanations,
we may perceive that all fractional and irrational results will be represented
in decimal fractions. Supposing each column to have forty discs, this extension
will be sufficient for all degrees of approximation generally required.

It will now be inquired how the machine can of itself, and without having recourse to the hand of man, assume the successive dispositions suited to the operations. The solution of this problem has been taken from Jacquard's apparatus[7], used for the manufacture of brocaded stuffs, in the following manner:-

Two species of threads are usually distinguished in woven stuffs; one
is the *warp *or longitudinal thread, the other the *woof *or
transverse thread, which is conveyed by the instrument called the shuttle,
and which crosses the longitudinal thread or warp. When a brocaded stuff
is required, it is necessary in turn to prevent certain threads from crossing
the woof, and this according to a succession which is determined by the
nature of the design that is to be reproduced. Formerly this process was
lengthy and difficult, and it was requisite that the workman, by attending
to the design which he was to copy, should himself regulate the movements
the threads were to take. Thence arose the high price of this description
of stuffs, especially if threads of various colours entered into the fabric.
To simplify this manufacture, Jacquard devised the plan of connecting each
group of threads that were to act together, with a distinct lever belonging
exclusively to that group. All these levers terminate in rods, which are
united together in one bundle, having usually the form of a parallelopiped
with a rectangular base. The rods are cylindrical, and are separated from
each other by small intervals. The process of raising the threads is thus
resolved into that of moving these various lever-arms in the requisite
order. To effect this, a rectangular sheet of pasteboard is taken, somewhat
larger in size than a section of the bundle of lever-arms. If this sheet
be applied to the base of the bundle, and an advancing motion be then communicated
to the pasteboard, this latter will move with it all the rods of the bundle,
and consequently the threads that are connected with each of them. But
if the pasteboard, instead of being plain, were pierced with holes corresponding
to the extremities of the levers which meet it, then, since each of the
levers would pass through the pasteboard during the motion of the latter,
they would all remain in their places. We thus see that it is easy so to
determine the position of the holes in the pasteboard, that, at any given
moment, there shall be a certain number of levers, and consequently of
parcels of threads, raised, while the rest remain where they were. Supposing
this process is successively repeated according to a law indicated by the
pattern to be executed, we perceive that this pattern may be reproduced
on the stuff. For this purpose we need merely compose a series of cards
according to the law required, and arrange them in suitable order one after
the other; then, by causing them to pass over a polygonal beam which is
so connected as to turn a new face for every stroke of the shuttle, which
face shall then be impelled parallelly to itself against the bundle of
lever-arms, the operation of raising the threads will be regularly performed.
Thus we see that brocaded tissues may be manufactured with a precision
and rapidity formerly difficult to obtain.

Arrangements analogous to those just described have been introduced into the Analytical Engine. It contains two principal species of cards: first, Operation cards, by means of which the parts of the machine are so disposed as to execute any determinate series of operations, such as additions, subtractions, multiplications, and divisions; secondly, cards of the Variables, which indicate to the machine the columns on which the results are to be represented. The cards, when put in motion, successively arrange the various portions of the machine according to the nature of the processes that are to be effected, and the machine at the same time executes these processes by means of the various pieces of mechanism of which it is constituted.

In order more perfectly to conceive the thing, let us select as an example
the resolution of two equations of the first degree with two unknown quantities.
Let the following be the two equations, in which *x *and *y *are
the unknown quantities:-

*x =*

__dn____' -__

*d*'*n**, and for*

*y*an analogous expression. Let us continue to represent by V

_{0}, V

_{1}, V

_{2}, &c. the

*n'm - nm'*

different columns which contain the numbers, and let us suppose that the first eight columns have been chosen for expressing on them the numbers represented by

*m*,

*n*,

*d*,

*m*',

*n*',

*d*',

*n*and

*n*', which implies that V

_{0 }=

*m*, V

_{1}=

*n*, V

_{2 }=

*d*, V

_{3 }=

*m*', V

_{4 }=

*n*', V

_{5 }=

*d*', V

_{6 }=

*n*, V

_{7 }=

*n*'.

The series of operations commanded by the cards, and the results obtained, may be represented in the following table:-

*m*,

*n*,

*d*,

*m*',

*n*'

*, d*', in the order and on the columns indicated, after which the machine when put in action will give the value of the unknown quantity

*x*for this particular case. To obtain the value of

*y*, another series of operations analogous to the preceding must be performed. But we see that they will be only four in number, since the denominator of the expression for

*y*, excepting the sign, is the same as that for

*x*, and equal to

*n*'

*m - nm*'. In the preceding table it will be remarked that the column for operations indicates four successive

*multiplications*, two

*subtractions*, and one

*division*. Therefore, if desired, we need only use three operation-cards; to manage which, it is sufficient to introduce into the machine an apparatus which shall, after the first multiplication, for instance, retain the card which relates to this operation, and not allow it to advance so as to be replaced by another one, until after this same operation shall have been four times repeated. In the preceding example we have seen, that to find the value of

*x*we must begin by writing the coefficients

*m*,

*n*,

*d*,

*m*',

*n*',

*d*', upon eight columns, thus repeating

*n*and

*n*' twice. According to the same method, if it were required to calculate

*y*likewise, these coefficients must be written on twelve different columns. But it is possible to simplify this process, and thus to diminish the chances of errors, which chances are greater, the larger the number of the quantities that have to be inscribed previous to setting the machine in action. To understand this simplification, we must remember that every number written on a column must, in order to be arithmetically combined with another number, be effaced from the column on which it is, and transferred to the

*mill*. Thus, in the example we have discussed, we will take the two coefficients

*m*and

*n*', which are each of them to enter into

*two*different products, that is

*m*into

*mn*' and

*md*',

*n*' into

*mn*' and

*n*'

*d*. These coefficients will be inscribed on the columns V

_{0 }and V

_{4}. If we commence the series of operations by the product of

*m*into

*n*', these numbers will be effaced from the columns V

_{0 }and V

_{4}, that they may be transferred to the mill, which will multiply them into each other, and will then command the machine to represent the result, say on the column V

_{6}. But as these numbers are each to be used again in another operation, they must again be inscribed somewhere; therefore, while the mill is working out their product, the machine will inscribe them anew on any two columns that may be indicated to it through the cards; and as, in the actual case, there is no reason why they should not resume their former places, we will suppose them again inscribed on V

_{0 }and V

_{4}, whence in short they would not finally disappear, to be reproduced no more, until they should have gone through all the combinations in which they might have to be used.

We see, then, that the whole assemblage of operations requisite for resolving the two[8] above equations of the first degree may be definitely represented in the following table:-

According to what has now been explained, we see that the collection
of columns of Variables may be regarded as a *store* of numbers, accumulated
there by the mill, and which, obeying the orders transmitted to the machine
by means of the cards, pass alternately from the mill to the store and
from the store to the mill, that they may undergo the transformations demanded
by the nature of the calculation to be performed.

Hitherto no mention has been made of the *signs *in the results,
and the machine would be far from perfect were it incapable of expressing
and combining amongst each other positive and negative quantities. To accomplish
this end, there is, above every column, both of the mill and of the store,
a disc, similar to the discs of which the columns themselves consist. According
as the digit on this disc is even or uneven, the number inscribed on the
corresponding column below it will be considered as positive or negative.
This granted, we may, in the following manner, conceive how the signs can
be algebraically combined in the machine. When a number is to be transferred
from the store to the mill, and *vice versa*, it will always be transferred
with its sign, which will be effected by means of the cards, as has been
explained in what precedes. Let any two numbers then, on which we are to
operate arithmetically, be placed in the mill with their respective signs.
Suppose that we are first to add them together; the operation-cards will
command the addition: if the two numbers be of the same sign, one of the
two will be entirely effaced from where it was inscribed, and will go to
add itself on the column which contains the other number; the machine will,
during this operation, be able, by means of a certain apparatus, to prevent
any movement in the disc of signs which belongs to the column on which
the addition is made, and thus the result will remain with the sign which
the two given numbers originally had. When two numbers have two different
signs, the addition commanded by the card will be changed into a subtraction
through the intervention of mechanisms which are brought into play by this
very difference of sign. Since the subtraction can only be effected on
the larger of the two numbers, it must be arranged that the disc of signs
of the larger number shall not move while the smaller of the two numbers
is being effaced from its column and subtracted from the other, whence
the result will have the sign of this latter, just as in fact it ought
to be. The combinations to which algebraical subtraction give rise, are
analogous to the preceding. Let us pass on to multiplication. When two
numbers to be multiplied are of the same sign, the result is positive;
if the signs are different, the product must be negative. In order that
the machine may act conformably to this law, we have but to conceive that
on the column containing the product of the two given numbers, the digit
which indicates the sign of that product has been formed by the mutual
addition of the two digits that respectively indicated the signs of the
two given numbers; it is then obvious that if the digits of the signs are
both even, or both odd, their sum will be an even number, and consequently
will express a positive number; but that if, on the contrary, the two digits
of the signs are one even and the other odd, their sum will be an odd number,
and will consequently express a negative number. In the case of division,
instead of adding the digits of the discs, they must be subtracted one
from the other, which will produce results analogous to the preceding;
that is to say, that if these figures are both even or both uneven, the
remainder of this subtraction will be even; and it will be uneven in the
contrary case. When I speak of mutually adding or subtracting the numbers
expressed by the digits of the signs, I merely mean that one of the sign-discs
is made to advance or retrograde a number of divisions equal to that which
is expressed by the digit on the other sign-disc. We see, then, from the
preceding explanation, that it is possible mechanically to combine the
signs of quantities so as to obtain results conformable to those indicated
by algebra[9].

The machine is not only capable of executing those numerical calculations
which depend on a given algebraical formula, but it is also fitted for
analytical calculations in which there are one or several variables to
be considered. It must be assumed that the analytical expression to be
operated on can be developed according to powers of the variable, or according
to determinate functions of this same variable, such as circular functions,
for instance; and similarly for the result that is to be attained. If we
then suppose that above the columns of the store, we have inscribed the
powers or the functions of the variable, arranged according to whatever
is the prescribed law of development, the coefficients of these several
terms may be respectively placed on the corresponding column below each.
In this manner we shall have a representation of an analytical development;
and, supposing the position of the several terms composing it to be invariable,
the problem will be reduced to that of calculating their coefficients according
to the laws demanded by the nature of the question. In order to make this
more clear, we shall take the following[10] very simple
example, in which we are to multiply (*a *+ *bx*^{1})
by (A + B cos^{1 }*x*). We shall begin by writing *x*^{0},
*x*^{1}, cos^{0} *x*, cos^{1 }*x*,
above the columns V_{0}, V_{1}, V_{2}, V_{3};
then since, from the form of the two functions to be combined, the terms
which are to compose the products will be of the following nature, *x*^{0
}.cos^{0} *x*, *x*^{0} .cos^{1}
*x*, *x*^{1}.cos^{0} *x*, *x*^{1}
.cos^{1} *x*, these will be inscribed above the columns V_{4},
V_{5}, V_{6}, V_{7}. The coefficients of *x*^{0},
*x*^{1}, cos^{0 }*x*, cos^{1 }*x *being
given, they will, by means of the mill, be passed to the columns V_{0},
V_{1}, V_{2} and V_{3}. Such are the primitive
data of the problem. It is now the business of the machine to work out
its solution, that is, to find the coefficients which are to be inscribed
on V_{4}, V_{5}, V_{6}, V_{7}. To attain
this object, the law of formation of these same coefficients being known,
the machine will act through the intervention of the cards, in the manner
indicated by the following table[11]:-

We may deduce the following important consequences from these explanations, viz. that since the cards only indicate the nature of the operations to be performed, and the columns of Variables with which they are to be executed, these cards will themselves possess all the generality of analysis, of which they are in fact merely a translation. We shall now further examine some of the difficulties which the machine must surmount, if its assimilation to analysis is to be complete. There are certain functions which necessarily change in nature when they pass through zero or infinity, or whose values cannot be admitted when they pass these limits. When such cases present themselves, the machine is able, by means of a bell, to give notice that the passage through zero or infinity is taking place, and it then stops until the attendant has again set it in action for whatever process it may next be desired that it shall perform. If this process has been foreseen, then the machine, instead of ringing, will so dispose itself as to present the new cards which have relation to the operation that is to succeed the passage through zero and infinity. These new cards may follow the first, but may only come into play contingently upon one or other of the two circumstances just mentioned taking place.

Let us consider a term of the form *ab ^{n}*; since the
cards are but a translation of the analytical formula, their number in
this particular case must be the same, whatever be the value of

*n*: that is to say, whatever be the number of multiplications required for elevating

*b*to the

*n*th power (we are supposing for the moment that

*n*is a whole number). Now, since the exponent

*n*indicates that

*b*is to be multiplied

*n*times by itself, and all these operations are of the same nature, it will be sufficient to employ one single operation-card, viz. that which orders the multiplication.

But when *n *is given for the particular case to be calculated,
it will be further requisite that the machine limit the number of its multiplications
according to the given values. The process may be thus arranged. The three
numbers *a*, *b* and *n *will be written on as many distinct
columns of the store; we shall designate them V_{0}, V_{1},
V_{2}; the result *ab ^{n}* will place itself on the
column V

_{3}. When the number

*n*has been introduced into the machine, a card will order a certain registering-apparatus to mark (

*n*- 1), and will at the same time execute the multiplication of

*b*by

*b*. When this is completed, it will be found that the registering-apparatus has effaced a unit, and that it only marks (

*n*- 2); while the machine will now again order the number

*b*written on the column V

_{1}to multiply itself with the product

*b*

^{2}written on the column V

_{3}, which will give

*b*

^{3}. Another unit is then effaced from the registering-apparatus, and the same processes are continually repeated until it only marks zero. Thus the number

*b*will be found inscribed on V

^{n}_{3}, when the machine, pursuing its course of operations, will order the product of

*b*by

^{n }*a*; and the required calculation will have been completed without there being any necessity that the number of operation-cards used should vary with the value of

*n*. If

*n*were negative, the cards, instead of ordering the multiplication of

*a*by

*b*, would order its division; this we can easily conceive, since every number, being inscribed with its respective sign, is consequently capable of reacting on the nature of the operations to be executed. Finally, if

^{n}*n*were fractional, of the form

*p*/

*q*, an additional column would be used for the inscription of

*q*, and the machine would bring into action two sets of processes, one for raising

*b*to the power

*p*, the other for extracting the

*q*th root of the number so obtained.

Again, it may be required, for example, to multiply an expression of
the form *ax ^{m }*+

*bx*by another A

^{n}*x*+ B

^{p }*x*, and then to reduce the product to the least number of terms, if any of the indices are equal. The two factors being ordered with respect to

^{q}*x*, the general result of the multiplication would be A

*ax*+ A

^{m+p }*bx*+ B

^{n+p }*ax*B

^{m+q }*bx*. Up to this point the process presents no difficulties; but suppose that we have

^{n+q}*m = p*and

*n*=

*q*, and that we wish to reduce the two middle terms to a single one (A

*b*+ B

*a*)

*x*. For this purpose, the cards may order

^{m+q}*m*+

*q*and

*n*+

*p*to be transferred into the mill, and there subtracted one from the other; if the remainder is nothing, as would be the case on the present hypothesis, the mill will order other cards to bring to it the coefficients A

*b*and B

*a*, that it may add them together and give them in this state as a coefficient for the single term

*x*=

^{n+p }*x*.

^{m+q}This example illustrates how the cards are able to reproduce all the operations which intellect performs in order to attain a determinate result, if these operations are themselves capable of being precisely defined.

Let us now examine the following expression:-

*n*is infinite. We may require the machine not only to perform the calculation of this fractional expression, but further to give indication as soon as the value becomes identical with that of the ratio of the circumference to the diameter when

*n*is infinite, a case in which the computation would be impossible. Observe that we should thus require of the machine to interpret a result not of itself evident, and that this is not amongst its attributes, since it is no thinking being. Nevertheless, when the cos[12] of

*n*= 1/0 has been foreseen, a card may immediately order the substitution of the value of p(p being the ratio of the circumference to the diameter), without going through the series of calculations indicated. This would merely require that the machine contain a special card, whose office it should be to place the number p in a direct and independent manner on the column indicated to it. And here we should introduce the mention of a third species of cards, which may be called

*cards of numbers*. There are certain numbers, such as those expressing the ratio of the circumference to the diameter, the Numbers of Bernoulli, &c., which frequently present themselves in calculations. To avoid the necessity for computing them every time they have to be used, certain cards may be combined specially in order to give these numbers ready made into the mill, whence they afterwards go and place themselves on those columns of the store that are destined for them. Through this means the machine will be susceptible of those simplifications afforded by the use of numerical tables. It would be equally possible to introduce, by means of these cards, the logarithms of numbers; but perhaps it might not be in this case either the shortest or the most appropriate method; for the machine might be able to perform the same calculations by other more expeditious combinations, founded on the rapidity with which it executes the first four operations of arithmetic. To give an idea of this rapidity, we need only mention that Mr. Babbage believes he can, by his engine, form the product of two numbers, each containing twenty figures, in

*three minutes*.

Perhaps the immense number of cards required for the solution of any
rather complicated problem may appear to be an obstacle; but this does
not seem to be the case. There is no limit to the number of cards that
can be used. Certain stuffs require for their fabrication not less than
*twenty thousand *cards, and we may unquestionably far exceed even
this quantity[13].

Resuming what we have explained concerning the Analytical Engine, we may conclude that it is based on two principles: the first, consisting in the fact that every arithmetical calculation ultimately depends on four principal operations - addition, subtraction, multiplication, and division; the second, in the possibility of reducing every analytical calculation to that of the coefficients for the several terms of a series. If this last principle be true, all the operations of analysis come within the domain of the engine. To take another point of view: the use of the cards offers a generality equal to that of algebraical formulae, since such a formula simply indicates the nature and order of the operations requisite for arriving at a certain definite result, and similarly the cards merely command the engine to perform these same operations; but in order that the mechanisms may be able to act to any purpose, the numerical data of the problem must in every particular case be introduced. Thus the same series of cards will serve for all questions whose sameness of nature is such as to require nothing altered excepting the numerical data. In this light the cards are merely a translation of algebraical formulae, or, to express it better, another form of analytical notation.

Since the engine has a mode of acting peculiar to itself, it will in
every particular case be necessary to arrange the series of calculations
conformably to the means which the machine possesses; for such or such
a process which might be very easy for a calculator may be long and complicated
for the engine, and *vice versâ*.

Considered under the most general point of view, the essential object of the machine being to calculate, according to the laws dictated to it, the values of numerical coefficients which it is then to distribute appropriately on the columns which represent the variables, it follows that the interpretation of formulae and of results is beyond its province, unless indeed this very interpretation be itself susceptible of expression by means of the symbols which the machine employs. Thus, although it is not itself the being that reflects, it may yet be considered as the being which executes the conceptions of intelligence[14]. The cards receive the impress of these conceptions, and transmit to the various trains of mechanism composing the engine the orders necessary for their action. When once the engine shall have been constructed, the difficulty will be reduced to the making out of the cards; but as these are merely the translation of algebraical formulae, it will, by means of some simple notations, be easy to consign the execution of them to a workman. Thus the whole intellectual labour will be limited to the preparation of the formulae, which must be adapted for calculation by the engine.

Now, admitting that such an engine can be constructed, it may be inquired:
what will be its utility? To recapitulate; it will afford the following
advantages: - First, rigid accuracy. We know that numerical calculations
are generally the stumbling-block to the solution of problems, since errors
easily creep into them, and it is by no means always easy to detect these
errors. Now the engine, by the very nature of its mode of acting, which
requires no human intervention during the course of its operations, presents
every species of security under the head of correctness: besides, it carries
with it its own check; for at the end of every operation it prints off,
not only the results, but likewise the numerical data of the question;
so that it is easy to verify whether the question has been correctly proposed.
Secondly, economy of time: to convince ourselves of this, we need only
recollect that the multiplication of two numbers, consisting each of twenty
figures, requires at the very utmost three minutes. Likewise, when a long
series of identical computations is to be performed, such as those required
for the formation of numerical tables, the machine can be brought into
play so as to give several results at the same time, which will greatly
abridge the whole amount of the processes. Thirdly, economy of intelligence:
a simple arithmetical computation requires to be performed by a person
possessing some capacity; and when we pass to more complicated calculations,
and wish to use algebraical formulae in particular cases, knowledge must
be possessed which presupposes preliminary mathematical studies of some
extent. Now the engine, from its capability of performing by itself all
these purely material operations, spares intellectual labour, which may
be more profitably employed. Thus the engine may be considered as a real
manufactory of figures, which will lend its aid to those many useful sciences
and arts that depend on numbers. Again, who can foresee the consequences
of such an invention? In truth, how many precious observations remain practically
barren for the progress of the sciences, because there are not powers sufficient
for computing the results! And what discouragement does the perspective
of a long and arid computation cast into the mind of a man of genius, who
demands time exclusively for meditation, and who beholds it snatched from
him by the material routine of operations! Yet it is by the laborious route
of analysis that he must reach truth; but he cannot pursue this unless
guided by numbers; for without numbers it is not given us to raise the
veil which envelopes the mysteries of nature. Thus the idea of constructing
an apparatus capable of aiding human weakness in such researches, is a
conception which, being realized, would mark a glorious epoch in the history
of the sciences. The plans have been arranged for all the various parts,
and for all the wheel-work, which compose this immense apparatus, and their
action studied; but these have not yet been fully combined together in
the drawings[15] and mechanical notation[16].
The confidence which the genius of Mr. Babbage must inspire, affords legitimate
ground for hope that this enterprise will be crowned with success; and
while we render homage to the intelligence which directs it, let us breathe
aspirations for the accomplishment of such an undertaking.

**Footnotes**

*an engine which can effect these four operations*can in fact effect

*every species of calculation*. The apparent discrepancy is stronger too in the translation than in the original, owing to its being impossible to render precisely into the English tongue all the niceties of distinction which the French idiom happens to admit of in the phrases used for the two passages we refer to. The explanation lies in this: that in the one case the execution of these four operations is the

*fundamental starting*-

*point*, and the object proposed for attainment by the machine is the

*subsequent combination of these*in every possible variety; whereas in the other case the execution of some

*one*of these four operations, selected at pleasure, is the

*ultimatum*, the sole and utmost result that can be proposed for attainment by the machine referred to, and which result it cannot any further combine or work upon. The one

*begins*where the other

*ends*. Should this distinction not now appear perfectly clear, it will become so on perusing the rest of the Memoir, and the Notes that are appended to it. - NOTE BY TRANSLATOR.

[2] The idea that the one engine is the offspring and
has grown out of the other, is an exceedingly natural and plausible supposition,
until reflection reminds us that *no necessary *sequence and connexion
need exist between two such inventions, and that they *may *be wholly
independent. M. Menabrea has shared this idea in common with persons who
have not his profound and accurate insight into the nature of either engine.
In Note A. (see the Notes at the end of the
Memoir) it will be found sufficiently explained, however, that this supposition
is unfounded. M. Menabrea's opportunities were by no means such as could
be adequate to afford him information on a point like this, which would
be naturally and almost unconsciously *assumed*, and would scarcely
suggest any inquiry with reference to it. - NOTE BY TRANSLATOR.

[3] See Note A.

[4] This must not be understood in too unqualified a manner. The engine is capable, under certain circumstances, of feeling about to discover which of two or more possible contingencies has occurred, and of then shaping its future course accordingly. - NOTE BY TRANSLATOR.

[5] See Note B.

[6] Zero is not *always *substituted when a number
is transferred to the mill. This is explained further on in the memoir,
and still more fully in Note D. - NOTE
BY TRANSLATOR.

[7] See Note C.

[8] See Note D.

[9] Not having had leisure to discuss with Mr. Babbage the manner of introducing into his machine the combination of algebraical signs, I do not pretend here to expose the method he uses for this purpose; but I considered that I ought myself to supply the deficiency, conceiving that this paper would have been imperfect if I had omitted to point out one means that might be employed for resolving this essential part of the problem in question.

[10] See Note E.

[11] For an explanation of the upper left-hand indices attached to the V's in this and in the preceding Table, we must refer the reader to Note D, amongst those appended to the memoir. - NOTE BY TRANSLATOR.

[12] *Classics* Editor's note: Lovelace has here
literally translated a printer's error that appeared in the original French
edition of the article. It should read ". . .in the __case__ of *n*
= 1/0. . ." The edition published in B.V. Bowden's __Faster than thought__
(New York, Pittman, 1953) corrects the mistake without comment. It has,
however, caused some to question Lovelace's mathematical competence (cf.
Stein, D. (1985). __Ada: A life and a legacy__. Cambridge, MA: MIT Press.).

[13] See Note F.

[14] See Note G.

[15] This sentence has been slightly altered in the translation in order to express more exactly the present state of the engine. - NOTE BY TRANSLATOR.

[16] The notation here alluded to is a most interesting and important subject, and would have well deserved a separate and detailed Note upon it amongst those appended in the Memoir. It has, however, been impossible, within the space allotted, even to touch upon so wide a field. - NOTE BY TRANSLATOR.