424 Prof. J. A. Fleming on the Propagation of 
The conversion of micro-microfarads to electromagnetic 
units of capacity involves the factor 10’. 
Hence the above may be written 
20000 x 10° 
—— a > - 5 - ° e 11 
Ut nu, : a 
Below is a Table showing the calculated values of the wave 
velocity W along the spiral for various observed values of 
the total capacity Cy (in m.mfds.) for different distances of 
the earth-wire. 
TABLE LT. 
Electric-wave velocity along a long Helix of 5000 turns, 
4*1 cms. diameter, and 200 cms. in length, calculated 
from the measured inductance and capacity of the 
helix. 
| 
Distance of earth- Capacity of helix in | Ware sorta hoe 
wire below helix. micro-microfarads. | f 4 
d. Cy ty 
1 centim. | 62:0 m.mfds. ) 180 x 10° 
~ centims. | es vs | 8 3 
O > 48-0 | 204 99 
re, Mors, ys. 
Ba ok 444 ,, WS 55 
ae cP ry 215, | 
| 7 ao 218 ,, 
ota Ae 221 *,, 
a / 404 ,, aes.) 
10 9 | 39°8 29 235 3) 
| Earth-wire removed. | sou) *,, Pad. gs 
| 
| 
| 
! 
Hence the wave-velocity along the helix when isolated in 
space approximates to 235 x 10° centimetres per second or 
135 part of the velocity of ether waves in free space or along 
a straight wire. 
Since the division of the total inductance and capacity by 
the length of the helix gives us only the mean inductance 
and capacity per unit of length, the above values of the wave- 
velocity are also mean values. 
The author has shown that the inductance per unit of 
length of a spiral is numerically equal to the square of the 
length of the wire wound on per unit length of the helix, 
and also that the capacity of a helix per unit of length 
