NO. H.] THE METEOROLOGICAL PERIODS IN THE ARCTIC SEA. 593 



The thermal amount of radiation from the sun on the unit of surface 

 perpendicular to the sun's rays is 1 



dg. = ^p'dt 



where C is the solar constant, referred to the mean distance of the earth 

 from the sun, square centimetre and minute of time, r the distance of the 

 earth from the sun, p the coefficient of transparency of the air, and s the 

 ratio of the mass of the atmosphere traversed by the ray to the mass tra- 

 versed by a ray from the zenith. I have assumed that C equals 3 gram 

 calories, p equals 0'75, and z equals cosec h (h the altitude of the sun) for 

 altitudes higher than 20. For lower altitudes I have taken MAURER'S values 2 

 for z, viz., for 5, 8'04, and for 0, 14-96, and taken the adopted values for 

 z from a curve. 



The radiation on a unit (sq. cm.) of a horizontal surface becomes 



n 

 dq = -3- p* sin h dt. 



I have taken the radiation of the sky from Clausius" numbers given by 

 J. HANN 3 , and extrapolated the numbers graphically, making the radiation 

 equal zero, when the apex of the twilight is below the horizon, a = ft -j- $ 

 + k + or = 16 38'. The table then stands thus: 



7t = --1638' -10 -5 5 10 15 20 25 30 

 p- 0-004 0-013 0-027 0-046 007 0'09 Oil 0'13 0'14 



The results of these computations are shown in the following Table. 



1 A. Angoi Recherches th^oriques sur la distribution de la chaleur a la surface du 

 globe. Annales du Bureau Central meteorologique de France. Annee 1883. Paris, 1885. 

 8 Angot. 1. c., p. 131. 

 8 Lehrbuch der Meteorologie, p. 42. 



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