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. 



[Bead 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 a 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 (b) 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 certainly ionise the gas through 

 which it passed. It was therefore decided to look first for 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 Rappo7'ts Congres de Physique, Vol. lit., Paris, 1900. 



