106 TAILS OF COMETS. 



plation of astronomers, the tails of comets are undoubtedly the 

 most perplexing. Now there is one feature of comets' tails that 

 has long since attracted attention, and will remind the reader of the 

 peculiarities common to the zodiacal and the auroral light. We re- 

 fer to the sudden changes of brilliancy, and the instantaneous 

 lengthening and shortening of these appendages. And the emi- 

 inent mathematician Euler was led by the observation of similar ap- 

 pearances to put forward the theory ' That there is a great affinity 

 between these tails, the zodiacal light, and the aurora borealis.^ 

 It is far from being unlikely that these long vexed questions — the 

 nature of the aurora, that of the zodiacal light, and that of comets' 

 tails — will receive their solution simultaneously;" and he further 

 adds : " I had scarcely completed the above pages when news was 

 brought from America that the spectrum of the sun's corona, as 

 seen during the recent total solar edipse, exhibited the same bright 

 lines as the aurora. Lastly, it has been found that the peculiar 

 phosphorescent light, sometimes visible all over the sky at night, 

 gives the same spectrum (very faint of course) as the aurora and 

 the zodiacal light. What we learn certainly, therefore, from the 

 facts above stated, is this — that substances of the same sort emit 

 the light of the aurora, of the zodiacal gleam, the tails of comets, 

 of the sun's corona, and of the phosphorescence which illuminates 

 at times the nocturnal skies. But when once we have reason — 

 as in the case of the aurora we undoubtedly have — to associate 

 electricity with any particular form of luminosity, we seem clearly 

 justified in extending the explanation to the same form of lu- 

 minosity wherever it may appear." 



Although I have already taxed your patience with long quotations 

 of such a strictly scientific character, I cannot conclude them 

 without giving Prof. Proctor's own deductions from this series of 

 arranged facts. He says : — 



" I believe that the key to the whole series of phenomena dealt 

 with above lies in the existence of myriads of meteoric bodies 

 travelling separately or in systems around the sun. They are 

 consumed in thousands daily by our own atmosphere. They 



