on Magnetic Storms. 66*3 



How outwards in all directions under its own mutual re- 

 pulsion : in the steady state (which is probably quickly 

 attained, while storm-producing streams often seem to 

 remain active for a month or more) the rate of escape of 

 the residual charge must equal the rate of emission of 

 the projected charge. The latter would therefore flow 

 through an " atmosphere " of charges of the opposite sign, 

 and if the velocity of escape of the latter were much less 

 than the velocity of projection of the locally-emitted charges 

 (as may well happen) the volume-density of charge in the 

 *• atmosphere " might, in spite of its greater extension, equal 

 or exceed that in the stream. The stream would in any case 

 draw the slower moving charges sideways from the "atmo- 

 sphere," and be itself slightly expanded sideways, until within 

 the enlarged stream the volume-density of charge was equal 

 to that of the " atmosphere " outside — the stream would then 

 be effectively neutral and would still convey charge mainly 

 of one sign to the earth without having suffered any serious 

 lateral dissipation. 



5. This establishes the possibility of the arrival of streams 

 such as I had contemplated : their origin, even their existence, 

 are matters concerning which little or no evidence is yet 

 afforded by our imperfect knowledge of solar physics. In this 

 respect the neutral clouds with which Prof, Lindemann deals 

 are on much the same footing. The real evidence for either 

 must at present be inferential, e. g. derived from the study 

 of terrestrial magnetism. Considered from this standpoint, 

 the stieam hypothesis seems to possess advantages over the 

 cloud theory. The particles of the two signs in the neutra 1 

 cloud are supposed to have the same velocity along the stream: 

 on nearing the earth they will be deflected in opposite direc- 

 tions in the earth's magnetic field. According to Stormer's 

 calculations re such corpuscular paths, the two sets of particles 

 should penetrate the earth's atmosphere (presumably to dif- 

 ferent levels) within two zones, one round each pole of the 

 magnetic axis, but so that the heavier particles fall much. 

 nearer the poles than the lighter : also, while entering the 

 atmosphere all round either pole, the two sets of particles 

 falling near each pole will fall preferentially on opposite 

 sides of that pole. The phenomena of aurorse and magnetic 

 disturbance are not yet sufficiently well observed in polar 

 regions to allow any decision to be arrived at, as to whether 

 these two kinds of effects, corresponding to the two kinds of 

 particles supposed present in equal numbers, actually occur ; 

 but until they have been observed it seems more in accordance 

 with scientific procedure to adopt an hypothesis in which the 

 phenomena to be explained depend on one set of particles 



2 X 2 



