714 



assistent at tlie Physical Laboratory, made at my request, using 

 the observatious of Hackspili. '). 



As to the density of the metal vapours on the sun, whicii give 

 rise to the finest lines in the solar spectrum, we may treat these 

 according to Lokentz '•') as being very small. H' p is the pressure in 

 mm. mercury of the metal vapoui', / the length of the layer that 

 is traversed by the rays, Lorentz tinds at 7*^6000' /;/<^0,0Ü15 

 or p/<^ 15000 depending on the suppositions made. For /r= 10' cm. 

 would follow p <^ 0,00015 mm. mercury in the latter case and 

 /J <^ 0,00015 X iO"" mm. mercury in the former one. To the men- 

 tioned pressures correspond the densities 9.10 "^^ and 9.10—1". 



Let be proportional to the density, then we should tind 



dX 



da 10». 9.10-13 



for a density 9.10-'« ^ = = 10-" at 644^ C. We shall 



dX 10-5 



suppose this number to be still valid at 6000°. 



For « = 10-1- and / = 6.10-'' cm. we then roughly titid from 



dv 

 equation '2) — = 50. This number and therefore the velocity 



dz 



gradient becomes 10' times smaller, if we take 10^" for the density 

 of the metallic vapour and still smaller, if we assign a higher value 



to — — thai) we did aboAC. 

 dX 



A few objections can be made to the application of the above 

 given discussion to the explanation of solar phenomena. I .shall 

 mention these shortly. 



Even if we confine ourselves to rays proceeding from one point of 

 the sun, there seems to be a dilïiculty in the fact, that while rays of a 

 definite wave length and definite direction are deflected away from 

 the objective, there are other rays of the same wavelength and 

 originally another direction, which are deflected towards the objec- 

 tive. This difficulty may be avoided by assuming a partition of 

 velocities symmetrical with respect to the line connecting sun and 

 objective. Then all rays that must be taken into consideration are 

 deflected, if now we had to consider the light from one point of 

 the sun only, we might directly conclude, that for the mentioned 

 small velocity gradients the deflection of the light rays must give 

 rise to observable phenomena. One of these phenomena would be 

 the occurrence of complicated changes closely connected with the 



1) Hackspill. Ann. de Gliim. et de Phys. (8) 28, 676 and 66f. 1913. 



-) H. A. LoRENTz. On the widtli of spectral lines. Tliese proceedings, 23, 470. 1914. 



