abstracts: physics 33 



During the month of April special simultaneous registration observa- 

 tions were made at Cheltenham, Maryland, and at Tucson, Arizona, in 

 cooperation with the magnetic work of Professor Birkeland at Khartum, 

 Africa, when stud3 r ing the zodiacal light. It was thought that the com- 

 parison of the magnetic curves at places so far apart might serve to 

 decide the question of the simultaneity or non-simultaneity of the 

 abruptly beginning magnetic storms. R. L. Faris. 



PHYSICS. — On the computation of the constant d of Planck's equation 

 by an extension of Paschen's method of equal ordinates. E. Buck- 

 ingham and J. H. Dellinger. Bulletin Bureau of Standards, 7: 

 393-406, 1911. 



Planck's equation for the intensity of radiation J, of wave length X, 

 from a black body at the absolute temperature 6 viz. 



J=C 1 [x 5 (e C2/X0 -l)]~ 1 



appears to represent very well the results of all known observations. 

 If X0 is not too large, the experimental facts are represented sufficiently 

 well by Wien's equation: 



/ = CiX-V C2/ ^ 



This equation defines an optical scale of temperature, which is used for 

 high temperature work. To make this scale fit the standard gas scale 

 of temperature within their common range of about 650° C. to 1650° C, 

 the constant c 2 must be known accurately. This constant may be deter- 

 mined by observing the distribution of energy in the spectrum of a 

 black body at a constant temperature, giving a so-called "energy curve." 

 From the two values of X corresponding to equal values of J on either 

 side of the maximum of the curve, <h may be calculated by an equation 

 due to Paschen provided the observed curve is representable by Wien's 

 equation. 



This paper extends Paschen's method, in two different ways, to apply 

 to curves for which Planck's equation must be used. The first method 

 consists in the substitution in Paschen's equation of corrected values of 

 the wave lengths read from the energy curve, the point of the method 

 being in the determination of these corrections. The second method 

 solves Planck's equation directly, obtaining an exact relation, which 

 may be simplified by justifiable approximation to a form the same as 

 Paschen's equation with a small correction term added. J. H. D. 



