170 



Capt. Abney and Col. Festing. 



[June 19, 



Turns of the 



screw of 

 thermopile. 



16 

 17 

 18 

 19 



20 



Table XIV continued. 



Platinum wire 



Ware-length. 



22,300 

 23,800 

 25,300 

 26,800 

 28,300 



lamp. 



4-5 



2-7 



1-0 



'5 







Carbon filament 

 lamp. 



5-0 

 3-0 

 1-0 



5 







The radiatioii curves of the two spectra are similar in every respect, 

 showing that the energies of the rays at different parts of the 

 spectrum bear the same proportion in the two cases. We have 

 already mentioned that the law that connects the volts and amperes 

 in a current passing through a carbon filament applies to platinum 

 wire. In Table XV we give the observed and calculated current 



Table XV. Platinum Lamp. 



together with the total radiation observations, and it will be seen in 

 fig. 5 that the curve becomes a straight line after the expenditure of 

 about 3 watts of electrical energy. We may, therefore, conclude from 

 these experiments that bright or dull carbon and platinum behave 

 similarly to one another in every respect as regards quality of 

 radiation. 



We would again refer to fig. 4 in which the line passing through 

 the maxima is produced below the last observed thermogram. This 



