168 Mr Richardson, On an attempt to detect radiation, etc. 
On an attempt to detect radiation from the surface of wires 
carrying alternating currents of high frequency. By O. W. 
Richardson, B.A., Coutts Trotter Student, Trinity College. 
\Read 6 May 1901.] 
This work was directly suggested by the theory of the 
mechanism of the conduction of electricity in metals recently 
put forward by Professor J. J. Thomson 1 . According to that view 
electric currents in metals are carried by negatively charged ions 
moving with a definite velocity under a given electric field. In 
the case of alternating currents of high frequency, almost the 
whole of the current is carried by a very thin ‘skin’ at the surface 
of the metal ; so that if the current is carried by ions they must 
be either much more concentrated or move with considerably 
greater velocities in the parts near the surface of the metal. In 
any case, since the current tries to get as far out of the metal as 
possible, we might expect the ions to be driven away from the 
surface, if sufficiently strong currents of very high frequency were 
employed. The experiments cannot be regarded as a crucial test 
of the theory since we do not know anything about the forces 
which tend to retain the corpuscles within the body of the metal. 
But it seemed that a positive result might reasonably be 
expected, and so the experiments described below were under- 
taken. 
On d priori grounds it seemed probable that the radiation to 
be looked for would be similar in character to that given out 
by radio-active substances. It might be constituted by either 
(a) charged ions moving with considerable velocity, or (6) some 
disturbance produced by the sudden stoppage or starting of such 
ions. The effect would therefore probably be of the nature of 
primary or secondary Rontgen rays. It would probably affect a 
photographic plate, and it would certaiuly ionise the gas through 
which it passed. It was therefore decided to look first lor a photo- 
graphic effect, and failing that a discharging effect emanating 
from the surface of the wire. 
The alternating currents were obtained by the discharge of a 
large induction coil, each terminal of which was connected to the 
inside of a small Leyden jar. The jars were insulated in paraffin 
and their outsides were connected through the wire or rod to be 
investigated. The primary current was furnished by six large 
1 Rapports Congres de Physique, Yol. nr., Paris, 1900. 
