NICHOLS. — THE VISIBLE RADIATION FROM CARBON. 



109 



have indicated by means of lighter lines the form of curve which might 

 have been expected had the type of isotherm which exists at lower tem- 

 peratures been maintained. 



Above 1-400° it was found impossible to obtain consistent readings on 

 account of the rapid disintegration of the carbon rods ; but I was able to 

 satisfy myself after repeated trials that at temperatures not far above 

 1500° this change in the character of the isotherms had progressed to the 



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point at which the yellow regions of the spectrum possess an ordinate 

 o-reater than that of the extreme red or of the blue or violet. At a tern- 

 perature about 300° below that of the acetylene flame, then, the spectrum 

 of the carbon rod was relatively weaker in the red, stronger in the yellow, 

 and weaker again in the shorter wave lengths than the spectrum of the 

 flame. There is no reason to suppose tliat had it been possible to heat 

 the rods to the temperature of the flame itself the law of increase of 

 intensity for the various wave lengths would have undergone such radical 

 modifications to bring the two spectra at that temperature into identity. 



