432 Prof. J. A. Fleming on the Propagation of 
centimetres. This inductance was associated with an ebonite 
condenser of 0°0015 microfarad capacity, and it was found that 
when the long helix was connected to this oscillating circuit 
with the far end earthed, that stationary oscillations were set 
up init which had a node at the centre of the helix. This was 
therefore the first overtone. From the capacity 0°0015 mfd. 
and inductance 12,077 cms., we find the frequency in the 
oscillating cireuit was 1:174x 10°. Since the wave-length 
is equal to the whole length of the helix, viz., 200 centimetres, 
it follows that the wave-velocity should be 
200 x 1:174 x 10°= 234°8 x 10° ems./sec. 
This, however, is almost exactly the wave-velocity calculated 
from the constants of the helix. 
Again, the capacity was increased to 0°006 microfarad, and 
it was then found that the stationary oscillation set up on the 
helix was the fundamental having an antinode at the centre. 
This capacity 0°006 mfd. and inductance 12,077 centims. 
corresponds to a frequency of 0°587x 10°, and the wave- 
length is 400 centims. Hence, here also the wave-velocity 
is 400 x 0°587 x 10°= 2348 x 10° ems ./sec. 
On taking a higher frequency still, it was found that an 
inductance of 22 000 ems. and a capacity of 0°00062 mfd. 
in the condenser circuit excited on the helix a wave of 
length 150 centimetres. This capacity and inductance corre- 
spond to a frequency of 1°37 x 10°, and this again to a 
wave-length of 150 cms. Hence the wave-velocity is 
205 x 10° ems./sec. Accordingly, here again we find that 
with increased frequency the velocity of the wave along the 
helix with a wooden core decreases. 
To eliminate all doubt as to the effect of the conductivity 
of the wooden rod, a pair of new helices of wire were con- 
structed, each consisting of a thick ebonite tube wound over 
with one layer of double silk-covered copper wire. 
These helices will be called Helix A and Helix B. 
The length of each tube was 215 cms., and outside diameter 
4:75 cms. The wire was No. 3058s.w.G., and after being 
wound on in closely adjacent turns was lightly varnished 
with shellac varnish made up with absolute alcohol. The 
lengths, diameters, and turns of each helix were as follows :— 
Helix A. Number of turns=5465. Length of helix= 
210 centimetres. Mean diameter of one turn 
= 4°78 centims. 
Helix B. Number of turns =5476. Length of helix= 
210 centims. Mean diameter of one turn=4°76 
centims. 
