222 The Microscope. 



in front of the machine this table is nearest you and the index 

 wheel is at your right hand. The screw is provided also with a 

 wheel and crank at the right of the index wheel by means of 

 which the screw may be revolved independently of the auto- 

 matic movement to be presently described. Each revolution of 

 the wheel is registered by an index on the right end of the ma- 

 chine, in appearance like the face of a watch. 



At the rear side of the machine and parallel to the screw is 

 a shaft attached by means of a pulley to a small water-motor. 

 Upon this shaft, which extends the greater part of the length of 

 the machine, is an eccentric which, with every revolution, moves 

 a rod carrying the diamond-holder at right angles to the axis of 

 the screw. By an ingenious mechanism,which is difficult to de- 

 scribe in words, but very simple when you see it, every 5th and 

 10th line may be made longer than the others, and every 10th' 

 line longer than the 5th. The diamond-holder is provided with 

 a screw with an index-head by means of which the diamond 

 may be set at any desired inclination, and there is a device for 

 lifting the diamond above the surface of the plate after a line 

 has been ruled, while it is moved forward preparatory to another 

 stroke. The shaft above described also has near its end, 

 two circuit-closers by means of which the circuits through 

 the electro-magnets, to be presently described, are closed and 

 broken, and also a cam which actuates the lever to be presently 

 described. 



Extending along the right side of the machine between the 

 cam above described and the index wheel, is what Prof. Rogers 

 calls his " Universal Ratchet," which he considers the key to the 

 problem of automatic ruling. The universal ratchet is only used 

 when spaces of 1-1000 inch or less are to be ruled, as, from the 

 following description, it will be obvious that by it the index of 

 the screw can be moved only a fractional part of a revolution. 

 When longer spaces are required the screw is turned by the 

 wheel and crank above described. 



This universal ratchet consists of a lever about two feet 

 long, upon the end of the short arm of which and in contact with 

 the edge of the index of the screw are two electro- magnets made 

 concave so as to fit accurately against the edge of the index 

 wheel. The long arm of the lever, which is moved by the cam 



