The first attempt to control the carried wheel in a key-driven machine is found in a patent issued to Bouchet in 1882 (see illustration on opposite page); but it was a Geneva motion gearing which, as is generally known, may act to transmit power and then act to lock the wheel to which the power has been transmitted until it is again to be turned through the same source. Such a geared up and locked relation between the numeral wheels, of course, made the turning of the higher wheel (which had been so locked) by another set of key-mechanism an impossibility. BOUCHET MACHINE The illustration of the Bouchet machine on the opposite page was reproduced from the drawings of the patent which is the nearest to the machine that was placed on the market. The numeral wheels, like most of the single-digit adders, are three in number, and consist of the prime actuated, or units wheel, and two overflow wheels to receive the carry of the tens. The units wheel has fixed to it a long 10-tooth pinion or rotor I, with which nine internal segmental gear racks L, are arranged to engage and turn the units wheel through their nine varying additive degrees of rotation. [Sidenote: _Description of Bouchet machine_] The segmental gear racks L, are normally out of mesh with the pinion I, and are fast to the key levers E, in such a manner that the first depression of a key causes its rack to rock forward and engage with the pinion I, and further depression moves the rack upward and rotates the pinion and units numeral wheel. It will be noted that this engaging and disengaging gear action is in principle like that of Robjohn. The transfer devices for the carry of the tens, as already stated, belong to that class of mechanism commonly known as the “Geneva motion.” It consists of a mutilated or one-tooth gear fast to the units wheel operating with a nine-tooth gear, marked D¹, loosely mounted on an axis parallel to the numeral wheel axis. Each revolution of the units wheel moves the nine-tooth gear three spaces, and in turn moves the next higher numeral wheel to which it is geared far enough to register one point or the carry. A circular notched disc, marked S, is fast to the units wheel, and the nine-tooth gear D¹, has part of two out of every three of its teeth mutilated or cut away to make a convex surface for the notched disc to rotate in.