Temperature of tlie Carbons of the Electric Arc, fyc. 37 

 FIG. 7. 



The numbers are scale divisions on the scale of the radio-micrometer, 

 and therefore represent the radiation in arbitrary units : 



+ pole. Radiation 60 2 and 67'1 



Mean = 637 

 pole. Radiation = 21 '8, 



so that the radiation from the hottest part of the + pole was about 

 three times as great as that from the hottest part of the pole. 



Taking the temperature of the former as 3300 C., this would give 

 a temperature of about 2350 C. for the latter. . 



In a case where a " blob " had formed on the pole, as in fig. 7, 

 the following readings were obtained : 



+ pole. Radiation 57'0, 56'0, 56'6, and 55'5 



Mean = 56'3 

 pole. Radiation of hottest part = 38*3. 



Again, taking 3300 C. for the former, this gives about 2700 C. 

 for the latter, or 350 C. higher than that of the pole just after 

 the arc is started. 



We may say, then, that if the temperature of the crater is about 

 3300 C., that of the carbon is ordinarily about 2400 C. in its 

 hotter parts. 



As for the temperature of the arc itself, we can say nothing. 

 Allowing the pale violet glow between the poles to fall on the aper- 

 ture of the radio-micrometer, we obtained deflections of from 1 to 

 2 per cent, of those obtained when the hottest part of the crater was 

 used, which seems to indicate a comparatively high radiative power 

 for the hot gases which lie between the carbon poles. 



