450 THE POPULAR SCIENCE MONTHLY. 



with an index, which may be slid in the direction of its length, and by- 

 means of which we can enter any number we choose. Each button is 

 connected by a pendent wire, with a ten-toothed pinion, below the 

 tablet. By the side of each of the pinions is a cylinder with a hori- 

 zontal axis, the length of which is the same with that of the grooving 

 above it. Each of the cylinders bears projecting, upon half the cir- 

 cumference, nine nerves of successively increasing length, from ^ to 

 3^0- the length, and the motion of each cylinder is commanded by a 

 horizontal shaft, which is turned by a crank. The cylinders make a 

 revolution with each turn of the crank, but the pinions advance, each 

 only according to the number of teeth marked by the corresponding 

 index. Pinions mounted on the same axis with the index transmit the 

 motion to the figure-bearing wheels of the reproducer, which is placed 

 under a metallic plate, prolonging the first one. Each turn of the 

 crank produces the successive terms of an arithmetical progression. 

 Suppose we wish to multiply 37,456 by 435. We bring down to zero 

 the figures opposite the openings in the i-eproducer by means of an 

 effacer, which is to be described. We write on the tablet the number 

 37,456 ; then turn the crank five times, when we will be able to read 

 through the opening the product of 37,456 by 5 ; to get the product 

 by 35, we would have to turn 35 times, but for an ingenious disposi- 

 tion by which we push the whole apparatus a notch to the right, and 

 turn three times, which gives the product we are seeking ; then push- 

 ing another notch to the right, and turning four times, we have the 

 product by 435. The function of the reverser may be best explained 

 by a comparison. SupjDOse a carriage of two wheels and an axle-tree, 

 and a person is riding upon it holding an opened umbrella. As long 

 as the umbrella is held straight over the middle of the axle, it does 

 not move ; incline it over one of the wheels, it begins to revolve ; in- 

 cline it over the other wheel, it will turn in the contrary direction, 

 while the carriage will be all the time going straight ahead. In the 

 arithmometer, the wheels of our carriage are replaced by twin-pinions 

 and the umbrella by the figure-bearing wheel of the reproducer. By 

 pushing on a little lever, we bring whichever pinion we desire into 

 gear with the figure-bearing wheel, so that each turn of the crank — it 

 always turning in the same direction — brings successively before the 

 openings numbers increasing or decreasing in an arithmetical progres- 

 sion, of which the common difference is marked on the abacus of the 

 tablet. 



Lastly, the effacer illustrates the advantage that may be drawn from 

 a broken tooth. Below each figure-bearing wheel is found, solid with 

 it, another smaller toothed wheel in which the tooth corresponding 

 with the below the peep-hole is suppressed. A roweled button pushes 

 along a rack, that keeps the wheel turning, till the moment when the 

 is to appear before the opening. The operation is performed with 

 extreme rapidity, and is one among many admirable details in the per- 



