ELECTRO-MOTIVE POWBE. 



second, and when the last division of the scale has been engraved, 

 it not only suspends its own action, but stops that of the electro- 

 magnetic machine by which it is impelled. These automatic 

 arrangements must not be regarded as mere mechanical super- 

 fluities, upon which the boundless fertility of invention which 

 characterises the genius of M. Froment has been lavished ; they 

 are of great practical value and importance. It happens, for 

 example, that in these delicate operations, the tremor of the 

 ground on which the workshop stands, produced by the movement 

 of vehicles of transport in the adjoining streets, aft'ects in a 

 sensible degree the motion of the cutting point. It is therefore 

 always preferable to execute the most delicate work in the dead 

 of the night. Now, by the automatic contrivances above men- 

 tioned, this can be accomplished without imposing on the super- 

 intendent the necessity of watching. A clock, provided with an 

 apparatus similar in principle to a common alarum, is put in 

 mechanical connection with the dividing machine, and is set so as 

 to start the machine at any desired hour. This being done, and 

 the limb to be divided being fixed upon the table under the 

 cutter, the apparatus may be left to itself ; the superintendent 

 may retire to rest, and at the hour of the night which has been 

 selected, the electro-motive machine will be started by the clock, 

 and the dividing engine will commence, continue, and complete 

 its work with the most admirable certainty and precision, and, 

 when completed, the electro-motive machine will be stopped, and 

 all reduced to rest. 



The magnitude of the dividing engine for microscopic scales, is 

 about 8 inches long by 6 inches wide, and 4 inches high. The 

 magnitude of the electro-motive engine necessary to drive it, 

 is not more than 4 inches square in its base, and 3 inches 

 high. 



It is scarcely necessary to observe, that the more minute class 

 of these scales can only be seen by the aid of a microscope of high 

 magnifying power. This will be easily understood when it is 

 considered that, in a space measuring a tentli of an inch in 

 length, there are in the more minute scales, 2500 divisions. Such 

 is, nevertheless, the precision of the execution, that when looked 

 at with a sufficiently high magnifying power, the lines exhibit the 

 most perfect evenness and regularity. 



13. Among the inventions of M. Froment, which may be also 

 seen in operation in his establishment, are two electric telegraphs, 

 one of which transmits its messages by enabling an operator at 

 one station to direct an index, which moves upon a dial-plate, to 

 any desired letter of the alphabet, those letters being engraved 

 around the dial like the hour-mark upon a clock or watch. The 

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