88 
MR. G. J. 'BURCH ON THE TIME-RELATIONS OF THE 
the bar sharply up against the stop G, and then swings under the table, oscillating 
about the loop at the end of C, as a centre. On its return, as it passes the vertical, 
the contact is broken, first at G, which determines the period of closure, and 
immediately after, before the electrometer has time to creep, at L, on the other 
side of the circuit. It is then caught in the hand of the operator. The closure may 
be maintained during any odd number of swings by pressing the thumb upon the 
bar C, directly it has made contact, so as to hold it firmly against the stop, releasing 
it directly the weight has passed under the table for the last time, thus leaving 
it free to break contact on its return. The duration of a single swing is calculated 
by taking the time of 50 complete oscillations with the aid of a stop-watch. By 
suitably regulating the length of the string D, the time of closure can be adjusted to 
any desired period from - 4 sec. to 10 secs. The accuracy of the instrument was 
verified by comparing the results obtained with different lengths of string. 
The object of the experiments was three-fold, viz. :— 
(A.) To compare the time-relations of charge and discharge. 
(B.) To ascertain the difference, if any, of the rate of movement when the meniscus 
was made to rise, i.e., to advance towards the tip of the capillary, and when it was 
caused to fall, i.e., to recede from the tip. 
(C.) To measure the effect of the change of internal resistance during an excursion. 
As the instrument was one of constant sensitiveness, this could be done by 
comparing the ratios of successive ordinates corresponding to the equal time-intervals 
given by 1, 3, 5, 7, etc., swings of the pendulum-rheotome, the mean of a number of 
observations being taken in each case. 
The rheochord was set so as to give an excursion as near as possible of the full 
length of the scale of the eye-piece micrometer—50 divisions—and the capillary w r as 
fixed so that a mark 20 divisions from the tip coincided with the top of the scale. 
A low power was used, and the actual range of the movement was much greater than 
is employed in physiological work. One series of observations was taken with an 
added external resistance of 60,000 ohms. For measuring the rate of discharge, the 
rheotome was made to close a short circuit between the terminals of the electrometer. 
In the following experiments, 
l = the distance of the meniscus from the tip of the capillary, in divisions of the 
eye-piece micrometer. 
y = the distance of the meniscus from its final position of rest after a closure 
of infinite duration. 
The period of closure is expressed in swings of the pendulum rheotome. 
The last column shows the ratio of each value of y to the one preceding it. 
“ Up,” means an excursion towa.rds the tip of the capillary. 
“ Down,” signifies an excursion away from the tip of the capillary. 
