267 



spark between two rounded ends of platinum wire % mm. diameter sepa- 

 rated a small fraction of a mm. The potential at the spark gap was not 



N 



5"0Sac. 



PLRTE.a. 



PLRTE.X. 



great enough to spark a distance of 14 mm. While working with this 

 apparatus a phenomenon occurred which shows how easily constant errors 

 may influence the result. The lead screen used to intercept the radia- 

 tion was suspended by cords to the top of the iron lamp chimney so as 



