200 THE SPLASH OF A DROP AND ALLIED PHENOMENA. 



flash tliat tlie splasli is viewed. The illumi nation is greatly helped by 

 surrounding- the i)lace where the splash and flash are produced by a 

 white cardboard inclosure, seen in fig. 2, from whose walls the light is 

 diflused. 



It will be observed that the time at which the spark is made will 

 depend on the distance that the sphere has to fall before striking the 

 plate D, for the subsequent action of demagnetizing F and pulling the 

 wire L out of the mercury in the cup H is the same on each occasion. 

 The modus operandi is consequently as follows: The observer, sitting 

 in comparative but by no means complete darkness, faces the appa- 

 ratus as it appears in fig. 2, presses down the ends A' B' of the levers 

 first described, so that they are held by the electro-magnet O (fig. 1). 



Fig. 2. Electric flash npparatus. 



Then he ijresses the lever IST P down on the electro-magnet F, sets the 

 timing sphere and drop in place, and then, by means of a bridge 

 between two mercury cups, short-circuits and thus cuts off the current 

 of the electro-magnet C This lets ofi' drop and sphere, and produces 

 the flash. The stage of the phenomenon that is thus revealed having 

 been sufficiently studied by repetition of the experiment as often as 

 may be necessary, he lowers the plate D a fraction of an inch, and 

 thus obtains a later stage. Not only is any desired stage of the phe- 



