THE AURORA. 25 



Euler was led by tlie observation of similar appearances 

 to put forward the theory " that there is a great affinity 

 between these tails, the zodiacal light, and the aurora 

 borealis" The late Admiral Smyth, commenting on 

 this opinion of Euler's, remarks that "most reasoners 

 seem now to consider comets' tails as consisting of 

 electric matter ; " adding that " this would account for 

 the undulations and other appearances which have 

 been noticed, as, for instance, that extraordinary one 

 seen by M. Chladni in the comet of 1811, when certain 

 undulatory ebullitions rushed from the nucleus to the 

 end of the tail, a distance of more than ten millions 

 of miles, in two or three seconds of time." To this 

 we may add the somewhat bizarre theory suggested by 

 Sir John Herschel, that the matter forming the zodia- 

 cal light is " loaded, perhaps, with the actual materials 

 of the tails of millions of comets, which have been 

 stripped of these appendages in the course of successive 

 passages round the immediate neighborhood of the sun." 

 Now, hitherto no comet with a sufficiently brilliant 

 tail for spectroscopic analysis has appeared since Kirch- 

 hoff 's invention of that mode of research. Already 

 our physicists had been looking forward anxiously for 

 the appearance of such a comet as Donati's or Halley's. 

 But Angstrom's recent discovery, and the evidence 

 which seems to associate the tails of comets with the 

 auroral and zodiacal lights, render our spectroscopists 

 doubly anxious to submit a comet's tail to spectroscopic 



