468 Prof. Bumstead and Mr. McGougan on Emission of 



plainly shown by a comparison of the results for platinum 

 with those for gold and aluminium given in the previous 

 paper. The platinum foil is so much thicker than the others 

 that the entire form of the curve is distorted. Moreover, in 

 the foregoing experiments, very few points on the curve were 

 taken, so that indeed it is only by courtesy that it could be 

 called a curve at all. For these reasons a much more careful 

 determination was undertaken by means of the apparatus 

 shown in fiV. 1. 



CENTIMETERS. 



A copper plug, P, 4 mm. in diameter, whose lower surface 

 is covered with polonium, is surrounded by a brass cylinder, 

 C, which limits the cone of the rays so that they fall com- 

 pletely within the brass ring, E, which supports the sheet of 



