Electric Waves along Spiral Wires. 439 
The conclusions which may be drawn from this research 
are as follows :— 
(i.) In the construction of inductances and helices for such 
experiments as are here described, they should be wound on 
ebonite and not on wooden cores. 
Gi.) Spirals of wire, if the turns are at all close, have less 
inductance for frequencies of the order of a million than for 
frequencies of the order of 100, on account of the dielectric 
current passing between the turns. 
(iii.) The best form to give to a standard of inductance 
for high frequency work is a single wire bent into a circle or 
a square. 
(iv.) The velocity of an electric wave along a closely 
wound helix of wire is measured by the reciprocal of the 
square root of the product of its capacity and inductance per 
unit of length. 
(v.) The distance from the open end of the helix to the 
first node is always much less than a quarter of a wave- 
length, in fact, nearly one-fifth of a wave-length. 
(vi.) The distance between the first and second nodes 
reckoned from the free or insulated end of the helix is one- 
half of a wave-length. 
(vu.) If the fundamental oscillation is set up in a helix by 
attaching one end to an oscillating circuit tuned to it, the 
wave-length is rather more than four times the length of the 
helix, but not five times. 
The above described apparatus can he used with some 
modification for the determination of the wave-lengths of 
the sther waves employed in Hertzian wave wireless 
telegraphy. 
The frequencies used for the above purpose lie generally 
between the limits of 0°5 x 10° and 3.x 10°. 
The following is the arrangement required (see fig. 5, 
Pl. XIII.). In all the transmitters now used for Hertzian 
wave-telegraphy there is an oscillating circuit consisting of 
an inductance, a capacity, and a spark-gap. ‘This is directly 
or inductively coupled to an aerial circuit A. One of the 
spark-balls $ should be earthed, and a point at the opposite 
end of the inductance T, should be connected to an insulated 
metal plate P,, which may be conveniently a zinc plate, 
30 cms. or 12 inches square. A long helix H is prepared 
which may be 2 or 23 metres in length, consisting of fine 
insulated wire wound in one layer on ebonite rods or tubes 
about 4 or 5 cms. in diameter. This helix is supported in a 
horizontal position and well insulated, and one end of the helix 
is connected to an insulated metal plate P, of the same. size 
2H 2 
