EXCURSIONS OF THE CAPILLARY ELECTROMETER. 
101 
which the electrodes are applied gradually rises to a negative maximum during the 
first phase, is reversed, and then, having become positive, gradually subsides. 
My present purpose is to show in what way the method of analysis described can be 
applied to the photographic records of the electrical response (which I shall hereafter 
speak of as the record or curve), so as to determine the exact time-relations of the 
changes above described. 
O 
With this view I propose to present to the Society certain specimen records, and to 
state the results obtained by the analysis of each. This result will be best expressed 
by a graphic denoting the actual differences of potential between (in) and (f) at suc¬ 
cessive times during the period of electrical change. 
It may be convenient at this point to describe in detail the method of analyzing 
such records as muscle curves, in which the electrical variations are of brief duration 
and not necessarily of constant intensity or of the same sign. 
It has been shown in the first part of this paper that it is not difficult to procure 
an electrometer of which the time-relations may be expressed by the formula y = ae~ ct , 
and that, with a circuit of suitable resistance, the movement of the meniscus will 
commence the instant that a difference of potential is communicated to the terminals, 
and cease the instant it is withdrawn. With such an instrument under such con¬ 
ditions, as was stated in my preliminary note “ On a Method of Determining the 
Value of Rapid Variations of a Difference of Potential by means of the Capillary 
Electrometer” (‘ Roy. Soc. Proc.,’ vol. 48, p. 92), “ the velocity with which the meniscus 
is moving at any instant is that with which it would start if the zero-line were moved 
to the level then occupied by the meniscus, and the difference of potential existing 
at the time between the terminals of the electrometer were suddenly introduced 
and made permanent. Thus, the total indicated difference of potential is made up 
of two parts, viz., the difference represented by the distance through which the 
meniscus has already moved, and that indicated by the velocity with which it is still 
moving.” 
In the analysis of muscle curves, as will be seen, the latter is usually many times 
greater than the former, except at the beginning, middle, and end of the curve where 
the tangent is at right angles to the radius vector, and the subnormal is zero. 
The method of analysis set forth in my preliminary note is, in consequence of the 
change in the apparatus already referred to, whereby the sensitive plate is made to 
describe an arc of the circle instead of travelling in a straight line, superseded by the 
far simpler one given in the present paper. The subnormal to the normal curve— 
and, consequently, to any curve—is a constant multiple of y, the distance of the menis¬ 
cus from the point of rest corresponding to the difference of potential existing at the 
time between the terminals of the electrometer. 
As has been already said, the value of this constant multiplier is influenced by the 
resistance of the circuit in each experiment, and the first step is to determine it for 
the particular resistance used. This was done for the muscle curves of which the 
