PROPERTIES OF THE LEAF OF DIONAEA. 
17 
that the surface oscillates in its own plane. If this surface is blackened., and a 
tuning fork is allowed to inscribe its vibrations on it during its swing, it is easy 
to determine the time occupied by the pendulum in accomplishing any given distance 
taken at any part of its course from the tracing. I have provided my pendulum with 
a fixed circular scale, on which each division is at such a distance from the next that 
the trigger in passing from one to the other occupies one hundredth of a second. 
Against this scale slide four keys, as seen in the drawing. Each key is so constructed 
Fig. 7. 
The Pendulum-Rheotome (represented as if in motion). 
The motion of the pendulum is from right to left. The detent (on the right) is provided with 
a wire, by means of which the pendulum can be “ let off ” by the observer at the galvano¬ 
meter, which must necessarily be at a distance. (From a photograph.) 
that the trigger in passing, opens it. By means of these four keys two circuits can be 
independently closed and opened one after the other, and the time of closing and of 
opening can be determined with great exactitude, according to the following plan 
(fig. 8). 
Provided that the events of which the time relations are to be investigated occur 
within a third of a second, this is an excellent form of rheotome. In opening a key 
of the kind employed no time is lost; consequently, the time-interval of closure of 
the circuit corresponds exactly to the distance between I. and II., or between III, 
mdccclxxxii. p 
