274 
IOWA ACADEMY OP SCIENCE 
surface of one of the plates, of which about 20 were larger than 0.007cm. 
as seen by the microscope. "When one of the plates was laid on the other 
there was complete insulation, i.e. when the condenser was charged the 
potential did not vary noticeably in five minutes. The observations are 
shown in the following table: 
Approximate potential across sul- 
phur particles. Volts 
Zero reading of electrometer, D^. 
Heading of electrometer when 
charges are mixed, Di 
Reading of electrometer when 
charges are mixed, D 2 
Capacity, e. s. u 
Mean distance 
4.3.4 3.4 1.8 0.6 
186 186 186 186 
310, 329, 313, 245, 247, 
286, 289, 286, 205, 201, 201 
228, 237, 234, 205, 206, 
225, 223, 226, 192, 193, 192 
36 32 40 28 
0.0044cm. 
These results indicate that the electrical method gives a shorter dis- 
tance than the diameter of the sulphur particles, but it was not certain 
if the few largest surplus particles might not crush or give or roll into 
the scratches under the pressure of the upper plate. Further it was 
not Clear what action so many small particles would have on the dielee- 
trict constant of the intervening space. 
Because the sulphur particles were not uniform in size and possibly 
not rigid, together with the difficulty of ridding of the moisture, I decided 
to try quartz fibres. A small fibre was broken into two parts and placed 
between the two surfaces. It was a day in early May when the humidity 
was low, and the fibres were not previously heated, except in the oxygen 
flame when blown. Nevertheless the insulation was regarded as perfect. 
The following are the observations with these* quartz threads separating: 
Approximate potential between plates, Volts 2 
n 1 320,319,317, 
D 2 209,208,208, 
Capacity 100 
Corrected capacity 97 
Mean distance 
0.9 
242, 245, 245, 244, 245 
195.5, 196, 195, 197, 195 
103 
100 
00151cm. 
Now the -size of the quartz fibres separating the planes as determined 
by the micrometer eyepiece on the microscope was 
.00165 ± .000086cm. 
This difference between the distance then varies by only about two wave 
lengths. But I found later in reading the size of fine fibres by the 
microscope, that it was much easier to err by obtaining values too large 
than too small. This experiment then leads to the conclusion that if 
there be a conducting atmosphere, that it must not extend out more than 
two wave lengths. 
