10 



CHAP. II. HIGH MAGNIFICATION CRESCOGRAPH 



to the requirement of the particular experiment. The 

 complete apparatus is seen in fig. 3, in which the revolving 

 wheel for actuating the oscillating mechanism is clearly 

 shown. 



I used at first a pair of parallel eccentrics, but in the 

 newest type of apparatus with improved to-and-fro sliding 

 arrangement, one eccentric is found to be quite sufficient. 

 A very important condition for success is the securing of 



Fig. 2. Mechanism for oscillation of plate. 



E, eccentric ; k, crank ; s, slide ; p, holder for glass plate g ; 

 L, recording lever. Clock releases string, c, for lateral move- 

 ment of the plate. 



perfect smoothness of movement during the oscillation of 

 the plate. A horizontal slide, moving on ball-bearings, 

 carries the vertical plate-holder. The slide is so perfect 

 in action that a puff of air is by itself sufficient to move 

 the free plate-carrier either backward or forward. The 

 plate may thus be maintained in its to-and-fro oscillation 

 with very little expenditure of force, and the power required 

 from the clockwork is therefore very small. In my later 

 instruments an electric oscillating device has been success- 

 fully employed, which simplifies the matter still further. 

 An electric current flows intermittently through a coil of 



