BLUE-VIOLET LIGHT IN THE SOLAR CORONA ON AUGUST 30, 1905. 331 



above inequality are about ten times as much as the range of the exponents, and we 

 may write 



(I), (4), and (5) give then, if C"' = l'5C", 



-f(p) = CV 8 l - - 



which stands for the light radiated and scattered at right angles to the radial 

 direction by the particles in unit volume at distance p from the sun's centre. 

 Considering that the second term is only a fraction of the polarised light and the 

 latter a fraction of the total light, F(p) f(p) nearly equals the first term. If there 

 were no light scattered by the particles but only radiated, the number of particles 

 per unit volume, N (p), would, by (1), be proportional to p(l 0'72p~ l )~ 4 5 . This 

 result differs from that derived by ARRHENIUS, who based his calculations on 

 T (p) = constant. 



10. Plea for Repetition of such Observations as contained in this Paper and for 

 Observations of the Light Polarised at Various Distances. 



(a) For wave-lengths 0'3 to 0'5 the radiation of a particle at h = 50 is 355 times 

 as great as that at h = 1000, while for wave-lengths 0'55 to 0'65 this ratio is only 70. 

 Blue-violet radiation is almost inversely proportional to the sixth power of the 

 distance of the particle from the sun's centre (see 9, 5), and for red-yellow radiation 

 the power is only 4'3. 



Hence if in addition to photographs on ordinary plates a series of photographs be 

 taken with a colour screen on a plate sensitized for red-yellow rays another formula 

 would be found which should lead (see last section) to the same number of particles 

 per unit volume as that belonging to blue-violet radiation. Two such series of 

 photographs, together with observations of the light polarised at various distances, 

 would thus decide the debated question whether the luminosity is actually caused by 

 minute particles which are heated to luminescence by solar radiation and which 

 scatter sunlight. 



(6) Though it is a fact that the brightness of the corona undergoes changes, we are 

 ignorant whether the intensity of the corona at a certain distance in terms of that at 

 unit distance is a constant or not. Inferences might be drawn from data such as 

 contained in this paper and belonging to a series of eclipses which would advance our 

 knowledge of the constitution of the corona and give us some idea of the causes which 

 produce it. It is, of course, necessary that the plates have on all occasions the same 

 relative sensitiveness in the different regions of the spectrum. (I employed Imperial 

 special rapid plates.) 



2 u 2 



