JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. I, SEPTEMBER 19, 1911. No 4. 



PHYSICS. — Note on graphic solutions of Wien's spectral equa- 

 tion. George K. Burgess, Bureau of Standards. 



The fundamental equation of optical pyrometry is that express- 

 ing Wien's law, 



h = C\~ 5 e~^ T 



which we may consider from three points of view: 



1. For the determination of the temperature 7\ or T 2 of a 

 black body from observations on the corresponding intensities 

 1 1 and /•> of light of a given wave length: 



*fa£«i-l (1) 



c h T, T x 



2. For the determination of the temperature T of a substance 

 whose absorption coefficient A\ (equal to 1 — R\ where R\ is 

 the reflecting power) for a given wave length X is known and 

 whose apparent temperature is S\ as given by an optical pyro- 

 meter using light of the same wave length X : 



±lnA x = --- (2) 



c T Sx 



3. For the determination of the temperature of a black body 

 from intensity observations at two wave lengths Xi and X 2 : 



&i£-5&^ + !(i-i) (3) 



I 2 Xi T\X 2 Xi/ 



The value of c is a constant that has been determined as lying 



105 



