Electric Waves along Spiral Wires. 431 
the other hand, the velocity obtained from the higher har- 
monics is decidedly less. As there can be very little doubt 
but that the values given in Table VII. for the inductances 
and capacities for the condenser circuit corresponding to 
each harmonic are substantially correct, the only conclusion 
which can be drawn is that the wave-velocity along the helix is 
in some way or other diminished as the frequency increases. 
After numerous experiments and measurements designed 
to eliminate other possible causes for this diminution, it was 
found that ordinary dry wood has decided conductivity for 
high-frequency currents of the order of 10°. This can be 
shown in the following manner. If a stationary oscillation 
is excited in the spiral and a vacuum-tube placed near to, 
but not at a node, it glows feebly. If then a thick sheet of 
ebonite is interposed it does not affect the glow. If, 
however, a wood board is interposed, the glow ceases. The 
wood has conductivity enough to act as a screen for high- 
frequency oscillations ; accordingly it appears that the wooden 
rod on which the silk-covered wire forming the helix is wound 
must have conductivity sufficient at or above a frequency 
of 10° to act as an earth-wire. 
On referring to Table III. it will be seen that as the earth- 
wire was brought nearer to the helix, the velocity of the wave 
along it decreased because the capacity of the helix was 
increased. 
When the earth-wire was removed, the velocity was 
235 x 10° cms./sec. as calculated from the capacity and in- 
ductance. When the earth-wire was brought within 1 cm. 
distance of the helix, the velocity fell to 180 x 10° cms./sec. 
Hence it is not inconsistent to conclude that for frequencies 
above 10° the capacity of the helix is increased by the growing 
conductivity of the wooden rod within it, and the wave- 
velocity gradually falls from 235 x 10° down to 180 x 10° or 
170 x 10° as the frequency is increased to obtain the various 
harmonics. 
To confirm the above results, experiments were also made 
with oscillations set up in the helix when the end remote 
from the condenser circuit was earthed. In this case the 
harmonics resemble those established in an open organ-pipe, 
and their frequency increases in accordance with the natural 
numerals, whereas with the far end of the helix insulated 
they follow the law of the odd numbers. 
A square inductance was made consisting of one turn of 
No. 14 copper wire bent into a square, of which the side was 
6 feet 114 inches in length, or 212 centimetres. The perimeter 
was 846 centimetres and the calculated inductance 12,077 
