30 1 On the Bed Protuberances seen on the Sun's Limb, 



pearances consistent with the presence of a very attenuated 

 atmosphere. 



If in such a search we are to be guided by terrestrial physics, 

 we must look to those phenomena which take place in our own 

 atmosphere at the greatest elevation above the surface of the earth. 



Now the aurora will undoubtedly occur to us as an appear- 

 ance which both observation and experiment induce us to t asso- 

 ciate with the extreme limits of our atmosphere. 



But before discussing the question whether the auroral light 

 presents those characteristics which observation has assigned to 

 the red protuberances, I may remark that there is another 

 reason, besides our unwillingness to extend the solar atmosphere, 

 which might induce us to resort to this explanation. 



The observations of General Sabine, combined with those of 

 Dr. Schwabe, give us good grounds for supposing that the sun 

 exercises a magnetic influence upon the earth. Now the writer 

 has endeavoured to show that the terrestrial aurora is the in- 

 duced effect in the upper regions of the atmosphere of small but 

 rapid changes occurring in the intensity of the earth's magnetism. 



These changes form what is known as magnetic disturbances, 

 and occur simultaneously with auroras ; and it has been shown 

 by General Sabine that these disturbances have a daily period, 

 thus discovering their dependence upon the sun, and also a ten- 

 yearly period coincident with that of the relative frequency of 

 sun-spots. There is therefore little doubt left in the mind 

 that these changes in the earth's magnetism are due to similar 

 changes in the sun's magnetic effect, and that both are connected, 

 directly or indirectly, with those spots which appear on the 

 surface of our luminary. 



But are we to imagine that those changes in the sun's mag- 

 netic effect which, acting through the earth, produce an aurora 

 in our atmosphere, have no similar effect upon his own ? 



Being convinced that we had here grounds for a hypothesis 

 regarding the red flames, I ventured to mention this suggestion 

 regarding their nature to General Sabine, and was much de- 

 ighted to learn that the same thought had also occurred to 

 him, which he expressed in the following words : — " May not a 

 solar aurora call forth simultaneous corresponding auroras in all 

 the planets, proportioned to their strength, although it may be 

 very difficult, if not impossible, for us to determine this by ob- 

 servation ? ; ' 



It would thus appear that, a priori, we have grounds for sup- 

 posing that phenomena similar to terrestrial auroras may occur 

 at the extreme limits of the solar atmosphere. 



The question now arises, Can we suppose the red names to 

 be these auroras ? have they the requisite characteristics ? 



