There are two distinct classes of operations which may be noticed in this Machine: the one that does the addition, properly speaking; and the other that records it by figures, in the very terms of common arithmetic. The first operation is the adding: which is performed by means of an endless geering chain, stretched round the wheels A B C D, ([fig. 1]) and over the two rows of smaller pulleys a b c d e f g h i; where, observe, that the chain is bent round the pulley A, merely to shorten the Machine, as otherwise the keys 1 2 3, &c. to 9, might have been placed in a straight line, and thus the bending of the chain have been avoided.
The chain, as before observed, geers in the wheels B and D, which both have ratchets to make them turn one way only. Now, the keys 1 2, &c. have pulleys at their lower ends, which press on the aforesaid chain more or less according to the number it is to produce, and the depth to which it is suffered to go by the bed on which the keys rest, when pressed down with the fingers. Thus, if the key 1 be pressed, as low as it can go, it will bend the chain enough to draw the wheel B round one tooth—which the catch E will secure, and which the wheel C will permit it to do by the spring F giving way. But when the key 1 is suffered to rise again, this spring F will tighten the chain by drawing it round the pulleys A and D, thus giving it a circulating motion, more or less rapid, according to the number of the key pressed. Thus, the key 5 would carry five teeth of the wheel B to the left; and the catch E would fix the wheel B in this new position: after which the spring T would tighten the chain in the same direction and manner as before. It is thus evident, that which-ever key is pressed down, a given number of teeth in the wheel B, will be taken and secured by the catch E; and, afterwards, the chain be again stretched by the spring F. It may be remarked, that, in the figure, all the keys are supposed pressed down: so as to turn the wheel B, a number of teeth equal to the sum of the digits 1, 2, 3—to 9. But this is merely supposed to shew the increasing deflexion of the chain, as the digits increase: for the fact can hardly ever occur. We draw from it, however, one piece of knowledge—which is, that should the eye, in computing, catch several numbers at once on the page, the fingers may impress them at once on the keys and chain; when the result will be the same as though performed in due succession.
Thus then, the process of adding, is reduced to that of touching (and pressing as low as possible) a series of keys, which are marked with the names of the several digits, and each of which is sure to affect the result according to it’s real value: And this seems all that need be observed in the description of this process. It remains, however, to describe the [5th. figure], which is an elevation of the edge of the keyboard, intended to shew the manner in which the two rows of keys are combined and brought to a convenient distance, for the purpose of being easily fingered.
We now come to the other part of the subject—that of recording the several effects before-mentioned. The principle feature in this part, is the System of carrying, or transferring to a new place of figures, the results obtained at any given one. This operation depends on the effect we can produce by one wheel on another, placed near it, on the same pin; and on the possibility of affecting the second, much less than the first is affected: Thus, in [fig. 3 and 4], ([Plate 42],) if A be any tooth of one such wheel, placed out of the plane of the pinion B, it will, in turning, produce no effect upon that pinion: but if we drive a pin (a) into the tooth A, that pin will move the pinion B one tooth (and no more) every time this pin passes from a to b. And if we now place a second wheel (F) similar to A, at a small distance from it, so as to geer in all the teeth of the pinion B, this latter wheel will be turned a space equal to one tooth, every time the pin a passes the line of the centres of the wheel and pinion A B, (say from a to b.) It may be added, likewise, that this motion, of one tooth, is assured by the instrument shewn at E D, which is called in French a tout ou rien, (signifying all or nothing) and which, as soon as the given motion is half performed, is sure to effect the rest: and thus does this part of the process acquire, likewise, a great degree of certainty—if indeed, certainty admits of comparison.