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SCIENCE. 



[N. S. Vol. XVII. No. 421. 



relation traceable either in any of the 

 regular fluctuations of the magnetic force, 

 or in those irregular ones which occur dur- 

 ing a magnetic storm. If the horizontal 

 force is increased in one part of the earth, 

 it is very apt to show a simultaneoiis in- 

 crease the world over, regardless of the 

 direction in which the needle may point 

 in various localities. It is hardly neces- 

 sary to add that none of the fluctuations 

 in terrestrial magnetism can be explained 

 on the hypothesis that either the moon or 

 the sun acts as a magnet. In such a case 

 the action would be substantially in the 

 same direction at the same moment the 

 world over. 



Such being the case, the question may 

 arise whether the action prodiicing a mag- 

 netic storm comes from the sun at all, and 

 whether the fluctuations in the sun's ac- 

 tivity, and in the earth's magnetic field 

 may not be due to some cause external 

 to both. All we can say in reply to this 

 is that every effort to find such a cause 

 has failed and that it is hardly possible 

 to imagine any cause producing siich an 

 effect. It is true that the solar spots 

 were, not many years ago, supposed to be 

 due in some way to the action of the planets. 

 But, for reasons which it would be tedious 

 to go into at present, Ave may fairly regard 

 this hypothesis as being completely dis- 

 proved. There can, I conclude, be little 

 doubt that the eleven-year cycle of change 

 in the solar spots is due to a cycle going 

 on in the sun itself. Such being the case, 

 the corresponding change in the earth's 

 magnetism must be due to the same cause. 



We may, therefore, regard it as a fact 

 sufficiently established to merit further 

 investigation that there does emanate from 

 the sun, in an irregular way, some agency 

 adequate to produce a measurable effect 

 on the magnetic needle. We must regard 

 it as a singular fact that no observations 

 yet made give us the slightest indication as 



to what this emanation is. The possibility 

 of defining it is suggested by the discovery 

 within the past few years, that under cer- 

 tain conditions, heated matter sends forth 

 entities known as Rontgen rays, Becquerel 

 corpuscles and electrons. I can not speak 

 authoritatively on this subject, but, so 

 far as I am aware, no direct evidence has 

 yet been gathered showing that any of these 

 entities reach us from the sun. We must 

 regard the search for the unknown agency 

 so fully proved as among the most impor- 

 tant tasks of the astronomical physicist of 

 the present time. From what we know of 

 the history of scientific discovery, it seems 

 highly probable that, in the course of his 

 search, he will, before he finds the object he 

 is aiming at, discover many other things of 

 equal or greater importance of which he 

 had, at the outset, no conception. 



In his study of what is going on among 

 the stars, even the astronomer may for a 

 time fail to grasp the true significance of 

 what he sees through leaving out of account 

 the vastness of the field which he is survey- 

 ing. A remarkable case of this is seen in 

 the case of the new stars which have been 

 known to burst forth from time to time. 

 In at least two notable cases of this kind 

 within the past ten years, such stars have 

 been found, within a few months after their 

 outburst, to be changed into or surrounded 

 by a nebula. Nothing could, at first sight, 

 seem more natural or easily explained than 

 this occurrence. To whatever cause we 

 may attribute such a catastrophe as the 

 sudden multiplication, within the period of 

 two or three days, of the light of a sun by 

 thousands of times, the cataclysm must re- 

 sult in throwing out a mass of incandescent 

 vapor, rising with great speed. This vapor 

 expanding on all sides, will appear to us 

 as a nebula surrounding the star and con- 

 tinually enlarging. That any difficulty can 

 stand in the way of this view will first ap- 

 pear Avhen we make an estimate of the prob- 



