Chemistry and Physics. 38T 



length of the second set of vibrations would be commensurate 

 with molecular dimensions : Can these vibrations be the Rontgen 

 rays? If so, we should expect them to be damped with such 

 rapidity as to resemble electrical impulses rather than sustained 

 vibrations. 



If we turn from the rays themselves to the effect they produce, 

 we find that the rays alter the properties of the substances 

 through which they are passing. This change is most apparent 

 in the effects produced on the electrical properties of the sub- 

 stances. A gas, for example, while transmitting these rays is a 

 conductor of electricity. It retains its conducting properties for 

 some little time after the rays have ceased to pass through it, but 

 Mr. Rutherford and I have lately found that the conductivity is 

 destroyed if a current of electricity is sent through the Rontgen- 

 ized gas. The gas in this state behaves in this respect like a very 

 dilute solution of an electrolyte. Such a solution would cease to 

 conduct after enough electricity had been sent through it to elec- 

 trolyze all the molecules of the electrolyte. When a current is 

 passing through a gas exposed to the rays, the current destroys 

 and the rays produce the structure which gives conductivity to 

 the gas ; when things have reached a steady state the rate of 

 destruction by the current must equal the rate of production by 

 the rays. The current can thus not exceed a definite value, other- 

 wise more of the conducting gas would be destroyed than is pro- 

 duced. 



This explains the very characteristic feature that in the passage 

 of electricity through gases exposed to Rontgen rays, the current, 

 though at first proportional to the electromotive force, soon 

 reaches a value where it is almost constant and independent of 

 the electromotive force, and we get to a state when a tenfold 

 increase in the electromotive force only increases the current by 

 a few per cent. The conductivity under the Rontgen rays varies 

 greatly from one gas to another ; the halogens and their gaseous 

 compounds, the compounds of sulphur, and mercury vapor, are 

 among the best conductors. It is worthy of note that those gases 

 which are the best conductors when exposed to the rays are 

 either elements, or compounds of elements, which have in com- 

 parison with their valency very high refractive indices. 



The conductivity conferred by the rays on a gas is not 

 destroyed by a considerable rise in temperature ; it is, for example, 

 not destroyed if it be sucked through metal tubing raised to a 

 red heat. The conductivity is, however, destroyed if the gas is 

 made to bubble through water ; it is also destroyed if the gas is 

 forced through a plug of glass wool. This last effect seems to 

 indicate that the structure which confers conductivity on the gas 

 is of a very coarse kind, and we get confirmation of this from the 

 fact that a very thin layer of gas exposed to the Rontgen rays 

 does not conduct nearly so well as a thicker one. I think we 

 have evidence from other sources that electrical conduction is a 

 process that requires a considerable space — a space large enough 

 to enclose a very large number of molecules. 



