Notices respecting New Books. 69 



spectrum of nature. But the necessary absolute coincidence was 

 subsequently found to be, if at all, only with some infinitesimally 

 faint and hazy band in the blue ; so that the whole expected 

 great discovery was, after all, a most extreme case of the play of 

 ' Hamlet ' not only without the part of Hamlet (the princely citron 

 line), but without the part also of the red-hauded old Xing — or the 

 " red line," which is the next most important feature of the aurora- 

 spectrum (a line, too, that is very like the well-known red hydro- 

 gen-line, yet most decidedly not it) : and nothing was left further 

 to claim identity of spectrum-place with, except an uncertain faint 

 shimmering of mere continuous spectrum in the sky-blue, which 

 might be any thing or nothing, and so caused Prof. Alexander 

 Herschel to exclaim, with Shakespearian pity, and full rounding off 

 of the chief characters in the play, "Alas ! poor ghost ! " 



Was there ever, then, such a call upon every one with a tele- 

 scope and every one with a spectroscope to join in the next cam- 

 paign, and endeavour to retrieve the future of observation and the 

 credit of spectroscopic science ? Never certainly in all the written 

 history of Aurora ; wherefore to aid in that good cause the Third 

 part of Mr. Capron's book goes largely into magneto-electric expe- 

 riments touching all sorts of possibilities affecting the anxious mys- 

 tery of the coming foe. 



Every one, we suppose, now looks on the Aurora as having some- 

 thing electric in its nature — as possibly a slow discharge of some 

 kind even of atmospheric electricity, but which, in place of the 

 discontinuous discharge of lightning common to warmer regions of 

 the earth, travels from closely abutting particle to particle of semi- 

 frozen vapour nearly uniformly and most extensively distributed 

 through the atmosphere of not exactly the Polar, but rather only 

 the proximately Polar regions of the earth. 



Such slow electric discharge, after once being set in action by 

 electricity, is also believed to be influenced in position and shape 

 by terrestrial magnetism. But no known artificial production of 

 any kind of electric light, with or without any magnetism that 

 can be put into it, will produce in the spectrum that wonder of 

 the present age, the auroral citron line. 



Nevertheless Mr. Capron has researched into this matter largely, 

 having fitted up a very powerful electromagnet and tried its effects 

 on the illuminations already electrically excited of various gas- 

 vacuum tubes, and with the effect often of changing the intensity, 

 colour, and shape of the light therein (as detailed through forty well- 

 filled pages of his book), but never of producing the auroral citron 

 line. 



Some grand experiments of a further kind have been imagined 

 by Mr. Henry B,. Procter, of Clemen sthorpe, North Shields, the 

 author of the excellent article on "Aurora'' 1 in the presently pub- 

 lishing edition of the 'Encyclopaedia Britannica;' and though they 

 are hardly likely to be tried soon, because they will inevitably 



