( 316 ) 
the rise in pitch of electromagnetically driven tuningforks when the 
intensity of the currents is increased; and also with the rise of the 
pitch of harmoniumreeds when the air-pressure is increased. Yet 
there is already some difference in the origin of these last two 
phenomena, so as to forbid anything more than considering the 
analogy. The only allowed consequence is, that the electrical system 
consisting of a capacity and a selfinduction does in this special case 
not vibrate in its proper period and that this proper period might 
only be expected to be brought about by a hypothetie infinitely 
small constant current through the are. 
Increasing the P. D. at the carbons seems to lower the pitch and 
at the same time to increase the intensity of the sound; if the P.D. 
rises too much the whistling ceases all at once. As I worked with 
a constant E.M.F. of 110 Volts from an accumulator-battery, the 
primary current strength was regulated by inserting resistance or 
withdrawing it from the circuit. When without changing the resistance, 
the P. D. at the carbons rises, the current falls off and so causes the 
frequency to diminish at the same time. Yet by keeping the current 
constant, by lengthening the arc and withdrawing resistance at the 
same time an unmistakable lengthening of the period may be observed. 
From the Tables 1—VI curves have been plotted connecting the 
frequency with the current-strength. 
It is not impossible, that a simple relation might express this 
connection. Yet an experimental formula as 
pHa+tbl+eP 
is only possible when / is negative; as in this case there is a mini- 
b 
mum for /= >— this formula does not seem to be very plausible. 
2 
I have also tried a quadratic expression connecting the steadying 
resistance with the frequency, but this did not give satisfaction. 
At last I found as the most simple formula and agreeing best 
with the observed results: 
logp=adbl, 
in which « and % are constants, p the frequency and / the constant 
current intensity. 
I found for series 1: 
