THE AURORA. 17 



nature of the as yet undiscovered interpretation of 

 Angstrom's researches would at present be an idle task, 

 perhaps. But one feature of the solar scheme with 

 which we cannot doubt that it will be found to be 

 associated, must be mentioned before we conclude. 



Of all the phenomena presented to the contempla- 

 tion of astronomers, the tails of comets are undoubtedly 

 the most perplexing. Their rapid formation, their 

 swift motions (if indeed we could believe that their 

 changes of position are due to a real transmission of 

 their material substance), and the enormous variety of 

 configuration and of structure which they present to 

 our contemplation, render them not merely amazing, 

 but altogether unintelligible. 



Now there is one feature of comets' tails which has 

 long since attracted attention, and will remind the 

 reader of the peculiarities common to the zodiacal and 

 the auroral light. We refer to the sudden changes 

 of brilliancy, the flickerings or coruscations, and the 

 instantaneous lengthening and shortening of these 

 mysterious appendages. Olbers spoke of s explosions 

 and pulsations which in a few seconds went trembling 

 through the whole length of a comet's tail, with the 

 effect now of lengthening, now of abridging it by several 

 degrees.' And the eminent mathematician Euler was 

 led by the observation of similar appearances to put 

 forward the theory f that there is a great affinity between 

 these tails, the zodiacal light, and the aurora borealisS 

 The late Admiral Smyth, commenting on this opinion 

 of Euler's, remarks that ( most reasoners seem now to 



C 



