AN APPARATUS FOR OBSERVING SPLASHES. 
13 
caused by the spring causes the wire M to be withdrawn from a 
cup of mercury N, and by this means the strong primary 
current of an induction coil is broken at the surface of the 
mercury, the volatilization of which renders the flash particularly 
brilliant without unduly prolonging its duration. It is this flash 
which is used for illuminating the splash. It is produced inside 
a white cardboard box or screen, shewn in the diagram in dotted 
outline, which serves greatly to increase the illumination. This 
box is provided, as shown, with suitable openings to permit the 
entry of the falling drop and the motion of the lever KK. The 
plate or liquid on which the drop is to fall is placed inside. 
In order to make an observation, the observer sits in an 
obscurely lighted room, facing the open side of this box or screen 
— on the remote side of the diagram — and looking at the place 
at which previous trial has told him that the drop will fall, and 
having placed the drop on the smoked watch glass A, and the 
ivory sphere on the ring B, he cuts off the current of the 
electro-magnet C by short circuiting it, which is done by con- 
necting the two mercury cups PP' by a wire bridge. This starts 
the fall, and, a moment later, he sees a particular stage of the 
splash lighted up. He then draws from memory what he has 
seen. If he is uncertain, he can repeat the experiment without 
altering the height of the plate D, when the same, or very nearly 
the same, stage of the splash will be again exhibited. 
If he wishes to observe a later stage, he lowers the block 
carrying the plate D, and then repeats the operation. The 
distance through which he lowers it affords a measure of the 
time-interval between the two stages. 
Since the current, whose interruption produces the illumina- 
ting flash, is only wanted when the flash is wanted, the wire 
EK, by which it passes, is so arranged that its end R does not 
quite reach the mercury cup S into which the current is led, so 
long as the lever KK is held down by the electro-magnet ; but on 
