Positive Electrification by Hot Metals, 



101 



The electroscope was observed with a microscope provided with 

 a scale in its eyepiece. It was found, on comparing the scale 

 of the electroscope with a multicellular voltmeter, that the divi- 

 sions were of approximately equal value throughout the scale, 

 very nearly one volt per division. The scale had 50 divisions. 



When the apparatus was filled with air at atmospheric 

 pressure a leak was observed at ordinary temperatures. This 

 effect is quite distinct from the effect discovered by Guthrie, 

 since it is observed equally whether the charge is + or — 

 (Wilson, loc. cit.), whereas Guthrie's effect is only obtained 

 with a + charge, unless the temperature is above a red heat. 

 To make this effect insensible the pressure was reduced to 

 1 cm. of mercury. The Guthrie effect is not apparently 

 much affected by moderate reduction of pressure, whereas 

 the effect investigated by Wilson is diminished nearly in the 

 same proportion as the pressure. 



The first experiments were made with a pure silver wire 

 in air at 1 cm. pressure. This was heated to successively 

 increasing temperatures, and the corresponding rates of leak 

 determined. These were practically uniform for different 

 parts of the electroscope scale. The results were : — 



Temperature.. 15° 202° 236° 265° 277° 287° 



Leak -14 -59 2-70 6'5 13-5 30-0 



Ksr. 2. 



30 



20 



10 



« 



* < 



H 



X 1 , i , 



JOC 



Temperature, centigrade. 



These results are plotted on the appended diagram (fig. 2). 



