of Gases exposed to Rontgen Rays. 255 



carbon dioxide, a gas of greater density. It is interesting to 

 observe that vapours like mercury and methyl iodide which 

 allow light to pass through freely are very opaque to Rontgen 

 radiation. 



Since the absorption of energy of the radiation varies with 

 the length of the gas traversed and with the conductivity of 

 the gas, it is very strong evidence that the discharge of 

 electrification by the Rontgen rays is due to a process going 

 on throughout the volume of the gas, and is not due to the 

 disintegration of charged dust from the electrodes. 



Cavendish Laboratory, December 28, 1896. 



Note on the preceding Paper, by J. J. Thomson. 



The connexion obtained by Mr. Rutherford between the 

 coefficient of absorption and the saturation current through 

 the gas admits of an interesting method of expression on the 

 theory that the Rontgen rays so far resemble light as to be of 

 the nature of an electromagnetic wave or impulse. We may 

 regard such a wave or impulse as consisting of groups or a 

 group of Faraday tubes travelling outwards through space. 

 These tubes are of equal strength, the strength of each corre- 

 sponding to the atomic charge carried by a univalent atom. If 

 a molecule of the gas through which the rays are passing gets 

 dissociated into ions by the electric field produced by the 

 tubes, one and only one of the tubes will get detached from 

 the group and will be anchored by having its ends attached 

 to the ions into which the molecule is dissociated. The dis- 

 sociation of one molecule, or the production of one positive 

 and one negative ion, will withdraw just one tube from those 

 in the group forming the Rontgen rays. Now Mr. Ruther- 

 ford's result, if we can extend it to all gases, shows that the 

 production of each ion corresponds to a weakening of the 

 Rontgen rays (by the same amount) whatever may be the gas 

 from which the ion is formed. The intensity of the rays is 

 supposed to be measured by the conductivity they produce in 

 a standard gas at standard temperature and pressure. Thus 

 Mr. Rutherford's result may be expressed by saying that the 

 weakening of the rays is proportional to the number of Faraday 

 tubes stopped ; and hence that the intensity of the rays is 

 proportional to the number of Faradav tubes. 



