336 Mr. J. R. E. Murray. On the Effect of Rontgen [Mar. 19 y 



and remained steady there. Separating the plates produced no 

 further deflection, which shows that the contact potential difference 

 "between the surfaces of the plates has been reduced to zero. This is 

 confirmed by the measurement, made by the null method, of their 

 contact potential, which is now 



+ 0-39 volt. 



§ 9. In the above experiment the plates were at about one centi- 

 metre apart. I now increased the distance between them to two, 

 then to live, and then to ten centimetres; but in spite of the fact 

 that in the last case the rays must have passed almost . entirely 

 through the air between the plates without striking on their surfaces,, 

 the electrometer always crept up from zero to — 039 volt in a minute 

 or two, and remained almost steady at that value. 



§ 10. In the above experiments there was no screen between the 

 vacuum bulb and the ebonite back of the tinfoil plate. To make 

 sure that none of the effects observed were due to ordinary electrical 

 disturbances I now placed a piece of tinfoil, in connexion with the metal 

 lining of the box containing bulb and coil, over the hole in the box 

 from which the rays issued. With the plates parallel to the rays 

 and at about one centimetre apart the electrometer rose, while the 

 rays were on, from zero to — 0*39 volt in two minutes and remained 

 steady there. This shows that the effects above described are due to- 

 the new rays, which can pass with ease through tinfoil, and not to the 

 more ordinary forms of electric radiation. 



§ 11. In order to find whether these phenomena were strictly com- 

 parable with the results which Lord Kelvin had got many years ago- 

 by connecting the plates through an electrolyte, I made several 

 experiments in which connexion was made by a drop of acidulated 

 water. 



Before doing so, however, I measured their potential difference by 

 the null method and found it to be 



+ 0-57 volt. 



This variation from previous determinations is due no doubt to the 

 influence of the atmosphere in tarnishing the plates. It is much less- 

 than the changes, due to that cause, which I have often found in 

 other experiments on contact electricity. I now joined the plates by 

 a drop of acidulated water while they were in connexion with the 

 electrometer only. The deflection at once rose from zero to 



-0-54 volt. 



I now separated the plates, but this did not cause any notable- 

 change in the deflection, though it tended slightly in the direction 

 which indicated that the contact potential of the plates had not been* 



