128 _ Mr. C. A. Chant on the Variation of Potential along 
The knobs B, C were not kept polished, and the spark was 
about 1-9 mm. long. 
For earth, in the case of wires of lengths 500, 1500, and 
2000 cms., A was joined immediately to a large sheet of tin 
which, along with about two square metres more of sheet 
metal, was firmly connected to a steam-heating radiator near 
by. For the wire 1000 cms. in length the connexion from 
A to the sheet of tin was about 75 ems. long. 
The wire joined to A in place of the earth connexion was 
precisely the same as that acting as antenna and attached 
to D: and in order to prevent inductive effects between 
these two wires the former was drawn up in a vertical 
direction by a cord over a pulley in the ceiling. 
The readings were taken at points, usually 20 ems. apart, 
from one end of the antenna to the other, the readings mm 
some cases beginning at the free end, in the rest ending at it. 
A general view of the results obtained is given m Table I. 
and fig. 3. In the table the distances of the minima from 
the free end are given in centimetres, and the less-marked 
minima are inclosed in brackets. In all the curves ordinates 
denote magnetometer-deflexions, abscissz distances from free 
end of wire. 
Tassie I. 
Distance, in centimetres, of mmima from 
free end of antenna. 
Length of 
antenna, ‘ 
ems. " B. Cc. | 
With earth connexion. | linge wire No earth connexion. 
b 
500 =| (175). None. 260. None. —— 
; 
1000 = (120), (375), (500). None.) (150), (660). None. 130, 425, 715, (1000?) 
4 
} 15300 |G2907. Nome PO LL. | dP eee 
6 
2000 | None. Cees 2 ae 
It is seen from the curves, that joining to earth one pole 
of the oscillator is equivalent to adding to that pole a wire 
similar to the antenna ; or, in other words, the earth acts 
like a plane mirror in optics. This view has been put 
forward by several writers, especially by Slaby*, when 
offering an explanation of his system of syntonic telegraphy. 
+ A. Slaby, Funkentelegraphie, 2nd ed. p. 86, and fol. Berlin, 1901. 


