ELECTRO-MOTIVE TOWER. 



the conducting divisions, the current is transmitted ; when they 

 touch the non-conducting divisions, the current is interrupted. 



Each of these three rollers e, f, g is connected by a conducting 

 wire with the conducting wires of two electro-magnets diame- 

 trically opposed, as is indicated in fig. 5, so that the current is 

 thus alternately established and suspended on the several electro- 

 magnets, as the conducting and non-conducting divisions of the 

 disc pass the rollers e, and g. 



10. M. Froment has adapted a regulator to this machine, which 

 plays the part of the governor of the steam-engine, moderating 

 the force when the action of the pile becomes too strong, and 

 augmenting it when it becomes too feeble. 



A divided circle in n, fig. 4, has been annexed to the machine 

 at the suggestion of M. Pouillet, by which various important 

 physical experiments may be performed. 



11. Of all the purposes to which this moving power is applied 

 in the workshop of M. Froment, the most beautiful is that of 

 making the divisions on the limbs and scales of astronomical and 

 geodesical instruments, and of instruments of precision in general. 

 The machines by which such divisions are engraved are automatic, 

 each receiving its motion from an electro-motive machine of 

 proportionate power and magnitude. 



The limb to be divided is fixed upon a horizontal table, which 

 receives a slow and intermitting progressive motion from a fine 

 screw. This screw itself is urged at intervals by a ratchet-wheel. 

 The catch or click by which this ratchet-wheel is driven, can be 

 so adjusted as to take one, two, or several teeth at each stroke, 

 and therefore to move the table carrying the limb through a 

 greater or less space, according to the magnitude of the divisions 

 to be engraved upon the scale. Over the limb to be engraved is 

 placed the point or edge by which the incision is produced, which 

 is either hardened steel or diamond. During the progressive 

 motion of the table carrying the limb, this cutter is elevated, so as 

 not to touch it. In the intervals during which the motion of the 

 table is suspended, the cutter descends upon the limb, and, being 

 pressed upon it with sufficient force, is drawn upon it in a 

 direction at right angles to the motion of the table, thus engraving 

 upon it the line which marks the division. Thus the motions of 

 the limb and the cutter are alternate, each being in action while 

 the other is at rest. The cutter is fixed upon an arbor which 

 derives its motion from the same crank which works the ratchet, 

 but its connection is arranged so as to give them the alternate 

 action just mentioned. 



By an arrangement provided in this arbor, a more extended 

 motion is imparted to the cutter at every tenth stroke of the 

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