1901.] Effect of Light and Electric Radiation on Matter. 161 



Negative Type. — Fig. 3 exhibits the effect on the negative type as 

 exemplified by Sn and Pb coated with Br. It appears that in these, 

 warmth is favourable to quick recovery. For in India with Pb coated 

 with Br the self-recovery was obtained with the greatest ease. Here 

 a more careful adjustment was necessary. At first the flash of radiation 

 produces a sudden increase of resistance, from which there is no im- 











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d) ( 





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50" 









3" 



6 



4" 



5" 



Time. 



Fig. 3. — Self-recovering Receiver exhibiting negative touch (increase of resistance 

 under radiation), (a), (b), (c), and (d) are the different stages of quickness of 

 recovery (from 50" to 6") in a brominated tin receiver ; (e) and (f) are the 

 records of a brominated lead receiver. 



mediate recovery, but an inspection of the galvanometer spot at once 

 makes it evident that some internal struggle has been going on ; the 

 spot trembles, and then after awhile the internal friction is overcome, 

 and the substance suddenly recovers. But soon after this preliminary 

 stage the recovery becomes perfectly automatic and instantaneous. 

 Each flash of radiation produces a responsive galvanometer twitch, 

 immediately followed by recovery. 



Some of the stages are well seen in the curves given. ! In (a) the 

 recovery takes place in 50 seconds ; in (d) in only 6 seconds, (e) and 

 {/) show recovery in lead coated with bromine. The recovery gradu- 

 ally became very quick, from 4 seconds to 3 seconds ; after that it was 

 too quick for record. 



In all the above cases it will be noted that the curve of recovery is 

 convex to the abscissa; ithat is to say, it is at .first very rapid, but in 

 the later stage it becomes slower. 



