68 Notices respecting JYeiv Books. 



spectrum. It had, too, in every auroral display a constancy and a 

 power which rendered almost needless the notation of any thing 

 else in the spectrum ; and every thing there did accordingly pale 

 its insignificant head to most observers ; while reported discovery 

 after discovery extended through the whole Solar system the glory, 

 unity, and rule of that one chief dominant citron line. It was 

 said, for instance, that it also characterized the whole of that mys- 

 terious and believed solar phenomenon of the night-sky, the zodia- 

 cal light — then that it was the chief external feature in the spec- 

 trum of the solar corona as seen in total eclipses, and proved a 

 perpetual aurora to be always environing the sun ; and then, coming 

 down to earth, that wondrous citron-line was found to be an iron- 

 line ; wherefore, behold, iron can give out a rarer, lighter, more 

 ascensional vapour than any gas known. 



All this ivoulcl have been, if the spectrum-place of the observed 

 line in each case had been really the same ; for spectrum-place, if 

 well measured, is just as absolute as stellar position by right ascen- 

 sion and polar distance. But, as time went on, the introduction 

 by successive observers of more of that marvellously discriminating 

 power " dispersion" (or the parent of all spectrum-place) soon told 

 another tale — declaring firstly that without a terrestrial aurora in 

 the sky there was no citron or any other bright line in the spectrum 

 of the zodiacal light, secondly that the solar corona-line did not 

 pretend to correspond with the aurora's grand citron line, but 

 with some faint subsidiary line suspected by some one and con- 

 firmed by none ; and, thirdly, the same coronal line, and still 

 more the true auroral line, did not either of them correspond in 

 place with the expected iron-line, and were essentially different in 

 physiognomy as well — this being the particular discovery and 

 clearing-up of Prof. Young, of Princeton, TJ. S., who does all things, 

 spectroscopic, well. 



Then, in that case, what does the all-important aurora citron- 

 coloured line correspond with ? 



That is exactly the question which Mr. Capron asks you and 

 me and every one to join him in trying, by night and by day, and 

 by every manner of means, to discover if we may ; for, far as he, 

 and they, and all of us have searched yet, there is nothing else in 

 heaven above or earth below which gives a line of that comparative 

 intensity in that particular spectrum- place. Every pure chemical 

 element known to science, and not a few compounds also, have been 

 burned either in flame, or furnace, or electric spark, whether ordi- 

 narily presenting themselves as solids, fluids, or gases ; but the 

 line is not there ; neither is it in the sun, nor in any star, nor in 

 any nebula whatever. 



The last work of the late eminent Professor Angstrom, who him- 

 self had, years before, discovered this puzzling citron aurora-line, 

 was to compare it with the spectrum of the light of the negative 

 pole in an air- vacuum tube illuminated by electric spark ; and he 

 thought that he had at last therein and thereby attained the aurora- 



