718 Prof. L. T. More on the Fatigue of 



A comparison of these results with those for the same plates 

 in pure air, shows that the presence of ozone in small quantities 

 does increase the fatigue. The difficulties explained when 

 hydrogen was employed do not apply here, and the separate 

 readings were quite accurate. Fresh surfaces of iron in air 

 experienced an increase in activity, and copper showed little 

 or no change, but on the addition of ozone there results for 

 both a small fatigue. But evidently no such abnormal effects 

 occur as Hallwachs found for ultra-violet light. 



Summary of Results. 



The preceding experiments prove that all the metals tried, 

 with the possible exception of copper and aluminium, experi- 

 ence a fatigue when subjected to Rontgen radiation for a long- 

 period of time, if their surfaces are not polished. The greatest 

 diminution in activity was found in iron and zinc, and amounted 

 to about 10 per cent, for a three-hour exposure to the rays. 

 The fatigue is not a permanent effect, as the plates recovered 

 their original activity after a comparatively short rest. 



When iron and lead are freshly polished, the secondary 

 radiation increases and reaches a maximum value after an 

 exposure of an hour or two ; the behaviour of nickel is 

 different, as there was no regular change in its radiation 

 during an interval of three hours. 



The effect of immersing polished plates in coal-gas, which 

 would probably form sulphides on the surface, is not noticeably 

 different from the action in air. An inert gas, like hydrogen, 

 apparently tends to prevent changes in activity. Lastly, 

 when ozone is added to the air surrounding polished iron and 

 copper plates, a considerable fatigue occurs, but not comparable 

 to the effect noted by Hallwachs. 



The explanation of these results is decidedly in favour of 

 the fatigue being caused by changes of the gas in or on the 

 plates, rather than to any change in the metals themselves. 

 It is impossible as yet to decide definitely whether this effect 

 on the adjacent gas-films is caused by an increased or diminished 

 power of absorption of the secondary rays, or whether it is due 

 to the formation or destruction of electrified double-layers. 



But the experiments indicate that a modification of an 

 electrified double-layer by the rays is the more probable of the 

 two. A metal whose surface has stood untouched for months, 

 diminishes in its secondary radiation from the beginning of 

 the bombardment by the Rontgen rays. Now we must 

 suppose that what condensed gas or double-layers may have 

 formed on the plate during the preceding months, will be in 

 such a sufficiently stable state as not to change appreciably 



