the Light emitted by Incandescent Zinc Oxide. 



23 



of which these curves give us definite graphical expression 

 are familiar phenomena. The fading away of the beautiful 

 white glow of the film into the greenish-yellow of the cooler 

 oxide, without the intermediate redness which most bodies 

 display as they pass from higher temperatures through the 

 range of temperature which goes by the name of the red heat, 



Fig-. 1. 



Fiff. 2. 



Fig. 3. 



25 



20 



IS 



10 



25 



IS 



1-0 



A.=.S// 



A =.#3,3 



\ =.46/ 



.4ZO 



70G" 800° 300° 1000° 800 s 900° 7000 s 800 s 9QCT I0OO" 



Fig. 4. Fig. 5. Fig. 6. 



Isochromatic Curves for Zinc Oxide and Platinum (700° to 1000°). 



is caused by the gradual overpowering of the rapidly diminish- 

 ing radiated light by that due to reflexion. A remarkable 

 feature brought out by these isochromatic curves is the per- 

 formance of the film between 800° and 880°. Within that 

 range the change of radiating-power increases but slowly as 



