278 



KNOWLEDGE. 



[December, 1903. 



bvpotheses we are to choose in order to explain this 

 quantitative discrepancy. On the one hand, it is very 

 conceivable tliat though the sunspot is directly the cause 

 of the terrestrial magnetic effect, it is not the size of the 

 spot tvhich is the determining factor so much as some 

 other characteristic less easily recognized. Thus both the 

 Storm Group of October 31 last, and the group of 18S2, 

 November 17, were distinguished by the number and vivid- 

 ness of the hydrogen reversals in their spectra, and it is 



1; I I I M I I I I r I I T I I I I f r f 



5. — Greenwich Earth Current Register. 

 Norember 1. 



1903, October 31- 



conceivable that such reversals may be significant of more 

 effective action than the mere extent of surface of the 

 group. On the other hand, it may be that the connection 

 between sunspots and magnetic storms is not direct but 

 indirect ; both being the effects of some one common cause 

 which, nevertheless, does not act upon sun and earth 

 always in the same proportion. But, m any case, whether 

 the connection be direct or indirect, whether it be imme- 

 diate or only secondary, there can be no doubt that it is 

 real, actual, and effective. 



[The Editors do not hold themselves responsible for the opinions 

 or statements of correspondents.] 



STELLAE SATELLITES. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — With reference to Mr. Holmes' letter in the 

 November number of Knowledge, there can Ise no doubt 

 whatever as to the existence of the satellite to Procyon. 

 It has been seen and measured l>y Barnard, Hussey,'See 

 and Lewis, as well as by Schaeberle. The following are 

 some of the measures made since its discovery : — 



Astronomical Joiimal, 540. 

 541, June 18, 1903. 



1898-213 : 326-0 : 4 83 



1899073 : 330-6 : 4-91 



1900055 : 336-0 : 509 , 



1902-241 : 3465 : 511 .JHussey (Lick Observatory 

 i BulletiH, No. 44). 



19031.54 : 351-03: 5 16 fBarnard {Astro Journal, 

 { June 18, 1903). 



It has therefore moved about 25° in five years, or 5*^ per 

 annum. It was also measured at Greenwich Observatory 

 in 1902. 



With reference to the double companion of Eigel, 



Burnham says (Publications of the Terkes Observatory, 

 Vol. I., 1900, p. 60), after describing his unsuccessful efforts 

 to divide the small star, " Since the foregoing was written I 

 have received the recent measures of Aitken and Hussey, 

 made with the great refractor at Mount Hamilton. There 

 is no longer any doubt of the duplicity of this star. It is 

 equally certain that the period will be very short — perhaps 

 shorter than that of any known system," and be adds : " It 

 is therefore practically certain that A and B C form a 

 physical system." A is the bright star, and B C the 

 double companion. The measures of B C referred to by 

 Burnham are as follow : — 



1898 87 : 178-0 : 0-16. 3 nights. Aitken. 

 189888 : 178-4 : 0-12i-. 1 \. Hussey. 

 189917 : 196-2 : 0-12. 1 „ Aitken. 



The components were probably near periastron wlieu 

 Burnham tried to measure the star in the years 1889-1892. 

 I should not have mentioned these stars in my paper if 

 there was any doubt as to their existence. 



Mr. Holmes is mistaken in thinking that I "use the 

 word brightness indifferently for quantity of light and 

 surface brilliancy." The term " brightness " in my paper 

 means " quantity of light," and not " surface brilliancy." 

 The latter is not referred to at aU in my paper, except in 

 the case of Sirius and its satellite, and then I use the terra 



" inherent light." .^ _ ^ 



" J. E. Gore. 



Dublin, November 3rd. 



RADIUM AND THE SUN'S HEAT. 



TO THE EDITORS OP KNOWLEDGE. 



Sirs, — It is supposed to be not yet settled whether the 

 energy of radium comes from within or without. Up to 

 now most has been heard in favour of the former view, 

 which has included the contention that nothing can be 

 done to a radium compound to lessen or destroy its radio- 

 activity. This, I think, I have experimentally disproved 

 {vide Chemical News, October 23rd, 1903, p. 206), and as 

 an advocate of the theory that radium compounds derive 

 their energy from without, as in other phenomena of 

 absorption of radiant energy, I ask whether the time is yet 

 ripe for cosmic hypotheses based on the opposite view ? 



Halifax, Yorks., William Ackrotd. 



November 2nd, 1903. 



PROTECTIVE RESEMBLANCE IN BUTTERFLIES. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — Mr. Rogers' letter in the September number of 

 Knowledge on protective resemblance in butterflies 

 opens up a fairly large question. In a note by Mr. 

 Carpenter, I see this resemblance is attributed to natural 

 selection both with regard to the Brazilian butterflies and 

 in the moths which assume a smoke -colour in our own 

 country. 



With regard to the former, it would be most interesting 

 to know how long a time was occupied in their becomino- 

 like the granite ; but with regard to the effects of the 

 smoke of London and other towns, such moths as hetularia 

 and abruptaria have certainly got darker in our own time, 

 which hardly coincides with the working of evolution, 

 which is generally so slow as to be almost imperceptible. 



In the Trans. Eut. Soc. Land., 1903, there is an article on 

 the experiments carried out by Prof. E. B. Poulton on the 

 colour-relation between lepidopterous larva? and their 

 surroundings. These exhaustive experiments fully prove 

 that the larvte of 0. hidentata and G. qnercifolia are so 



