EXCURSIONS OF THE CAPILLARY ELECTROMETER. 
99 
The following 1 curves are given as examples of the effects of overshooting. The 
actual difference of potential employed was not ascertained owing to the instrumental 
difficulties referred to, which were not noticed till the conclusion of the experiments. 
No. 305. Fig. 7, Plate 3.—Artificial spike, given by an upward excursion lasting O'0052 sec., followed 
by a downward excursion lasting 0'004 sec. 
The second phase is slightly rounded at the beginning, showing that the full 
velocity was not attained immediately. The slight pause at the end of the fall, before 
the slow return to zero, is probably due to “ stickiness ” of the tube. (Compare also 
No. 299 where there is evidence of <£ stickiness ” during the swiftest part of the 
movement). 
No. 307. Fig. 8, Plate 3.—Artificial spike, as before, but in the reverse direction. 
In this case, the second phase begins sharply at its full velocity, but at the end of 
it the mercury has continued to move, not so rapidly as when the current was on, but 
still, more quickly than it would have done had the electrometer been simply 
discharging itself. 
No. 309. Fig. 9, Plate 3.—Excursion produced by a single current lasting 0'006 sec. 
Here the meniscus overshot the mark to the extent of 07 millim. in an excursion, 
the full height of which would have measured 80 millims. on the photograph, and 
which had only risen 7 millims. when the current was checked. The analysis shows 
that the second rheochord somehow became connected and furnished a current in the 
opposite direction of about one-fourth of the difference of potential of the first— 
possibly one of the leads might have touched the rheotome. 
It will be noticed that even this overshooting is under 1 per cent, of the total 
normal excursion, and that the time which elapsed between the withdrawal of the 
electromotive force and the cessation of the movement, was only about 0‘002 sec. 
These three jahotographs illustrate the form of overshooting, which I consider to be 
due to the elasticity of the meniscus, for, if it were true overshooting of the column, 
then the retardation of the return movement should be visible in the case of the 
reversed spike (No. 307, fig. 8) ; but this was only seen with much stronger currents. 
On the other hand, the sudden checking of an upward excursion, about three times the 
size of this, caused the meniscus to throw off a globule of mercury. 
In the preceding experiments, there was no external resistance. The effect of 
introducing a coil of 10,000 ohms is shown in the next example. 
No. 299. Fig. 10, Plate 3.—Downward excursion produced by a single current of short duration. 
External resistance = 10,000 ohms. 
In spite of the difference of potential being greater than in any of the preceding 
experiments, there is practically no overshooting, and the curve of discharge is 
perfectly normal. The subnormal to the curve was too great to be measured on the 
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