1004.] 



On the Electric Equilibrium of the Sun. 



497 



will be driven away with the greatest force from the sun if 

 its circumference is just as great as the wave-length of the radia- 

 tion. The wave-length of the maximal radiation of the sun is about 

 - 5 \x. Therefore the optimal dimension for a drop, that is 

 driven away by the pressure of radiation, will be about O06 /x. If 

 we suppose a specific weight of the drop like that of water, the 

 repulsive force for a perfectly reflecting drop amounts to about ten 

 times its weight. For a perfectly black drop it is half as great. Now, 

 most drops are neither perfectly reflecting nor perfectly black. Most 

 fluids absorb nearly completely the non-luminous radiation, and reflect 

 a part of the other. An appreciation of these two factors leads to the 

 estimation that the effect for the translucent fluids will be about half 

 as great as for a perfectly black body, i.e., about 2*5 times 

 greater than the gravity against the sun. Such a particle will move 

 away from the sun with 1 "5 times greater speed than that calculated 

 above, i.e., it will reach the earth in about 46 hours. 



Of course, there may be represented speeds that are more than the 

 double this for drops of low specific weight (compounds of carbon and 

 hydrogen). On the other hand, the speed may be extremely little (or 

 negative), for drops of high specific weight (e.g., gold). This will also 

 be the case for great or very small drops, as Schwarzschild has shown. 



These figures have recently acquired a great interest through the 

 discussion by Ellis, Maunder, and Eicco of the connection between 

 sunspots and magnetic storms. Eicco had already, in 1892, stated 

 that in six cases of very strong magnetic storms, these appeared 

 in mean 45*5 hours after the passage of a great sunspot over the 

 central meridian of the sun. In one case the difference of time was 

 only 20 hours. 



From the researches of Ellis and Maunder it appears that the mag- 

 netic storms commence in mean 26 hours after the great groups of sun- 

 spots, which probably caused them, had passed the central meridian of 

 the sun. Eicco applies a correction to these figures. He says that in 

 mean the great magnetic storms, quoted by Ellis and Maunder, lasted 

 for 33 hours, and therefore it is natural to assume that the maximum of 

 the magnetic storm, which will probably fall near its middle, arrives 

 1 6 '5 hours after its commencement. It will, therefore, be nearly true that 

 the maximum of the magnetic storms observed by Ellis, came 

 26 + 16*5 = 42*5 hours after the passage of the corresponding spot 

 through the central meridian of the sun. The figure very 

 nearly coincides with those of Eicco and also with that calculated 

 above. Eicc6 also makes the observation that the velocity of 

 the small particles, which in my opinion cause the auroras and 

 the magnetic storms, is of the same order of magnitude as the 

 observed velocity with which the cause of these perturbations moves 

 from the sun. 



