418 Prof. J. A. Fleming on the Propagation of 
H. C. Pocklington has treated the matter theoretically, 
and shows that the velocity of the wave along the axis of the 
spiral should be under some conditions less than that along a 
straight wire *. 
As the production of stationary waves on spiral wires has 
found practical application in connexion with Hertzian Wave 
Wireless Telegraphy, particularly in apparatus for syntoni- 
zation, it seemed desirable to investigate a little more closely 
the actual facts as a basis for further analysis. The following 
form of apparatus was therefore arranged, which is very 
suitable for the metrical study of stationary electric waves. 
On a long circular-sectioned wooden rod was uniformly 
wound a close helix of silk-covered copper wire. The bare 
wire was No. 32 S.w.G. in size, and the covered wire was 
0'4 mm. in diameter. It was laid on in one single layer of 
5000 turns. The length of the helix was 200 ems., and had 
therefore 25 turns of wire per centimetre. The outside 
diameter of the helix was 4:1 cms., and the diameter of the 
circular axis of each single turn was 4°096 cms. 
The electrical resistance of the wire at 15° C. was 153°2 
ohms. This helix was supported horizontally in a wooden 
frame at a height of 45 centimetres above the table, and 
parallel with it was stretched a bare platinoid wire 0°2 mm. 
in diameter, which could be connected to the earth or 
removed. The distance between the helix and this bare wire 
was ascertained by a scale placed at each end of the spiral. 
As this bare wire was connected to the earth, it will be called 
the “ earth-wire.” 
One end of the helical wire was attached to an electric 
circuit consisting of a condenser or a pair of leyden-jars, a 
thick bare copper wire wound in a spiral on a boxwood 
cylinder, having a sliding contact, thus forming a variable 
inductance ; and also a spark-gap included in a closed iron box. | 
The spark-balls were connected to an induction-coil capable 
of giving a 10-inch spark. The electrical arrangements were 
as Shown in fig. 1 (PJ. XIIJ.). The connecting wires joining 
the condenser, spark-gap, and variable inductance were formed 
of thick, insulated, stranded 19/16 copper cables. Parallel 
to the long helix, and at a distance of 15 cms. above it, was 
arranged a boxwood scale divided into centimetres. 
When the induction-coil was set in action, electrical 
oscillations were generated in the leyden-jar circuit, and 
by a suitable adjustment of the variable inductance in 
* “ Electric Oscillations in Wires,” H. C. Pocklington, Proc. Camb. 
Phil. Soe. vol. ix. p. 324, Oct. 25, 1897. 
