94 



REPORT — 1878. 



1 Arithmometre ;' * another is the Reducing Bar used by Mr. Babbage.f In 

 the second place, the carrying has to be provided for just as in ordinary 



Fig. 2. 



Fig. 3. 



D 



i: 



J? 



x> 



V- 



tv 



dj 



f 



addition of numbers. Taking account of all this, it follows that by 

 separating the counting on the whole into counting on figure by figure, 



* Let ZO (fig. 2) be a plate with ten ribs of different lengths, Aa, Bb, . . . . K7i 

 soldered on it. Let Mw. be a square axis on which the wheel N is made to slide by 

 the fork P. Then, supposing N to have teeth which can engage in the ribs Aa, Sec, 

 when the plate is pushed past the wheel N, the number of teeth through which the 

 wheel N, carrying with it the shaft Mm, is made to rotate, depends upon the number 

 of ribs in which it engages, and this depends upon how far along the axis N is made 

 to slide by means of the fork P. If this fork is set opposite the line marked 3, Mm 

 will turn through a space equivalent to 3 teeth. If a wheel, keyed to the shaft Mm, 

 be geared to other wheels, this enables us to add any digit to any number at a 

 single motion of the plate, by simply changing the position of P to suit the digit 

 required. This is the principle used in Thomas's arithmometre, only that there the 

 traversing plate is replaced by a rotating cylinder. 



t Suppose Aa, Bb, . . . . F/ (fig. 3) to be a series of racks passing hrough mor- 

 tices in a plate aw, and meeting a series of spur-wheels mounted loos<> n a shaft, so 

 that each wheel gears with one of the racks at the line pq, and that 11 the whole 

 series can be thrown in or out of gear together. Starting with them out of gear, 

 let the racks be drawn out through the plate <rz as indicated. Next throw the shaft 

 pq into gear, and then press a plate PQ against the ends of the racks, pushing them 

 back until the plates PQ and sez meet. Then each wheel aa jiq will turn through 

 the number of teeth corresponding to the original projection of the racks. In this 

 way, if the wheels on pq stood at any given number, say 543243, we should have 

 added 314236 to them, and they would then stand at the sum of these two numbers, 

 namely, 857479. This, it will be observed, makes no provision for carrying. PQ is 



