llieory of Magnetic Storms. 683 



the ions would gain enough energy from the field to ionize 

 by collision after one free path. Since the main constituent 

 -above a height of 10 7 cm. must be He, A =4 and V = 20'5, 

 -so that if Alt is of the order 10 7 and T greater than 100°, 

 P must less than 2300 volts or 7*7 E.S.U. The above value 

 of 11" 1 P may therefore be considered quite reasonable, in 

 fact one may deduce from this that k Y is probably of the 

 order of magnitude of 1/2. 



In this case the mass striking the earth is roughly 

 6 . 10 7 grammes. The total mass in the cloud, whose radius 

 was found above to be of the order 10 n cm., would therefore 

 be l'l . 10 12 grammes, by no means an excessive quantify. Jt 

 corresponds, near the sun's surface at the density estimated 

 above for complete ionization, to a diameter of about 2 . 10 9 cm. 

 or nearlv 1' which is of the right order of magnitude. 



It has been assumed throughout that Dr. Chapman's con- 

 clusion. is correct, namely that radial motion of the charge on 

 the earth is sufficient to account for the magnetic phenomena. 

 If one assumes, as he does, that the charges rapidly spread all 

 over the surf ace of the earth, as seems probable on accountof 

 the high mobility at such low pressures, there would seem no 

 reason to expect other phenomena than those he accounts 

 for. Changes in the electrostatic potential gradient ob- 

 viously cannot be caused by the two layers of opposite sign. 

 On the other hand, the maonetic effect of the radial flow 

 which occurs as they recombine must be the same as that 

 found by Dr. Chapman when his layer of a particles expands. 

 In both cases there may be a certain difficulty in explaining 

 the sudden inception of a storm, though this point could 

 only be studied with the help of actual records. Apart from 

 this, no real objections appear to exist in the theory set forth 

 above. Though the premises throughout are too uncertain 

 to allow one to claim that the quantitative results confirm 

 the theory, they do not seem in any way inconsistent either 

 with one another or with the accepted laws of physics. 



Summary. 

 It is shown that existing stream theories of magnetic 

 storms, more especially that worked out by Dr. Chapman, 

 .are untenable, because : — 



They require incredible radioactivity on the sun. 

 Even if this be granted, the particles could not remain 

 together on their way from sun to earth on account of 

 electrostatic repulsion. 

 Even if such a beam of charged particles could exist, it 

 could not impinge on the earth after the first few 

 seconds on account of the earth's charge. 



