14 Bumstead— Heating Effects produced by Eontgen Rays 



deflection. This was sluggish in comparison with that pro- 

 duced by the rays, and (as might have been expected from 

 varying air currents in the room) was irregular and somewhat 

 erratic in its course. In one respect, however, the behavior 

 was consistent; if the lamp was left glowing for one or two 

 hours, the radiometer always returned to the neighborhood 

 of its zero-point and staid there until the lamp was turned off. 

 It then made another slow and wandering excursion in the 



Cm. 













































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6 

































































































































































































































































































































A 



final 



es 











































































































































































































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-8 























































































-10 













































opposite direction (repulsion by zinc) and eventually again 

 returned to the middle of the scale. The application of ice to 

 the aluminium window also caused repulsion by the zinc. 



The determination of the different rates of heating and cool- 

 ing of the two strips furnished the explanation of this behavior. 

 While the window and adjacent parts of the case are slowly 

 warming up, they radiate to the two strips more and 

 more, and cause the temperatures of the latter to rise steadily ; 

 but the lead having a smaller time-constant than the zinc, has 

 the higher temperature and maintains it until the amount of 

 radiation reaching the strips no longer varies with the time — 



