m6 Prof. S. Chapman : A Note 



numerical estimates of mine concerning the density &c. o£ 

 the supposed stream, that if composed solely of a-particles 

 {or a fortiori if composed solely of negative electrons), it 

 would dissipate itself sideways by mutual repulsion before it 

 could take effect on the earth : and proposes in place of the 

 stream an ionized but electrically neutral cloud projected 

 from the sun. 



3. I concur in his conclusion that such streams as he contem- 

 plates would dissipate themselves as he describes, and though, 

 as he recognized, I do not lay great stress on the numerical 

 estimates referred to, I do not think they can be modified so 

 seriously as to affect this conclusion. On the other hand, 

 I think it is unnecessary, in order to overcome this objection, 

 to resort to his alternative hypothesis, nor does the latter 

 commend itself to me on its own merits. The difficulty to 

 which Prof. Lindemann has usefully drawn attention can be 

 met without departing from my original theory: in the latter 

 I regarded as the essential feature of the stream the con- 

 veyance of electric current, which implies that, if charges 

 of both sign are present, those of one kind preponderate 

 either in density or (since both are moving in the same 

 direction) in velocity, in order that the earth may receive 

 charges " mainly or entirely " of the same sign. At times 

 the qualifying words quoted may have been omitted for the 

 sake of brevity, and the impression conveyed that I regarded 

 the stream as consisting strictly of like charges, but if so 

 this was unintentional : and similarly I had never definitely 

 come to a decision (as in § 7 I now do) concerning the sign 

 of the preponderant charge. On the other hand, it is fair to 

 state that till the appearance of Prof. Lindemann's article 

 I had not recognized the absolute necessity for the presence 

 of both kinds of particles in the stream. The stream must 

 be practically neutral electrostatically, and this condition is 

 fulfilled if the volume density in it is the same for both kinds 

 of charge. It is needless to require the charges also to have 

 the same velocity, as he does, and there are definite reasons 

 against making the assumption (§§ 5, 6). 



4. On the other hand a stream such as I proposed, caused 

 by the emission of particles mainly or entirely of one sign 

 from some locally disturbed area of the sun, could easilv 

 adjust itself so as to become electrostatically neutral, while 

 at the same time the neutral stream might convey a current to 

 the earth in which the number of charges of one sign greatly 

 preponderated. The ejection of one kind of charge from 

 one region of the sun would leave the sun charged with the 

 opposite sign, and this charge would presumably distribute 

 itself uniformly over the sun with great rapidity, and then 



