PROCEEDINGS OF THE FoLYTECJIKIC ASSOCIATIOX. 909 



line. But the bright line on the spectrum of the aurora held a posi- 

 tion which belongs to no known element; it does not exist on the 

 earth. The experiments were carefully repeated by Angstrom, by 

 Otto Struve, and by Mr. Plnmmer, always with the same result ; we 

 are entirely ignorant of the nature of the substance to whose incan- 

 descence, or illuminating power, the aurora owes its brilliancy. 



Another still more remarkable discovery has been made. Ever 

 since the discovery of the zodiacal light by Cassini, it has been an 

 object of great interest to astronomers. Such men as Humboldt and 

 Sir John Herschel sanctioned M'ith their authority the tlieory in 

 regard to it, that the appearance is due to the light reflected from a 

 multitude of minute cosmical bodies traveling round the sun within 

 the orbit of the earth. The zodiacal light shines so taintly that it 

 was supposed its spectrum could not be rendered visible, and if it 

 were, a reproduction of the commot solar spectrum was confidently 

 anticipated by the advocates of the theory. 



Angstrom succeeded in obtaining the spectrum of the zodiacal 

 light, and that also presents but a single line. This line is the 

 identical line wdiich is seen in the spectrum of the aurora. There- 

 fore the gleani'of zodiacal light, and tlie flash of the aurora are due 

 to the same sort of electric discharge, taking place in the same 

 medium and' dependent upon an element which does not exist on 

 the globe. Here we seem to hold the key for the explanation of 

 many phenomena which have long been perplexing the scientific 

 world. Comets give the spectrum of the incandescent vapor of car- 

 bon, indicative of intense heat even when as in Winneke's comet, 

 they are farther from the sun than the earth is. The action of the 

 sun in exciting electric discharges would solve this and similar 

 mysteries. It has long been considered that the peculiarities of 

 comets' tails were dependent upon electrical action, Euler asserted 

 more than half a century ago that comets' tails have something in 

 common witli tlie aurora and the zodiacal light, We are safe in 

 prophesying that the next long-tailed comet that sweeps our sky will 

 have the devoted attention of all the cclel)rated physicists on the 

 globe. 



How stranger than any dream of a poet's fancy it would be, if 

 the most mysterious phenomena which have puzzled the brains of 

 the men of science should be discovered, at very nearly the same 

 time, to be due to the same cause, the all-powerful magnetism of the 

 sun, and that it is the manifestation of this wonder-working agent 



