NATURAL PHILOSOPHY. 135 







dro?en, are but imperfectly diactinic, and so arrest these extreme rays 

 of energy '.' Xot that sulphuretted hydrogen, or any compound bodv, 

 can be .-upposed to exist upon the solar surface. The elements th'Te, 

 iiiii-t .-t uid too much aloof, by the mutual hate of the fierce heat, to 

 unite themselves in alliances with each other. It may be, however, 

 that conditions unknown to us alter or modify the terrestrial law of de- 

 crease of heat. 



!i -ecmed, however, an object of great interest to know if similar 

 photographic spectra could be obtained of the stars. Mr. Higgins and 

 Dr. Miller have already been successful in photographing the more re- 

 frangible portion of the spectra of Sirius and Capella. 



\r : - Observations on Spectral Ana';i*i..< I;/ Prof. Plucker. The 

 following new vu>ws respecting spectral analysis were presented to the 

 liriti-h A ociation by Prof. Plueker : " It is generally admitted now," 

 he --lid. --that every gaseous body rendered luminous by heat or elec- 

 tricity sends out a peculiar light, which, if examined by the prism, 

 gives a well-defined and characteristic spectrum. By such a spectrum, 

 by any one of its brilliant lines, whose position has been measured, 

 you may recognize the examined gas. This way of proceeding con- 

 stitutes what i.s called spectral analy.-is, to which we owe, until this 

 day, the discovery of three new elementary bodies. In order to give 

 to spectral analysis a true and certain basis, you want the spectrum of 

 each elementary substance. Most recently, some eminent philosoph< 

 in examining such spectra, met with unexpected diiliculties, and doubts 

 arose in their minds again-t the new doctrine. These doubts are un- 

 f junded. The fact is, that the molecular constitution of gases is mueh 

 more complicated than it has been generally admitted to be till now. 

 The spectra, therefore, always indicating the molecular constitution of 

 gases, ought to be more complicated also, than it was thought at first. 

 Uy th< :isiderations, a new importance, a rather physical one, is 



given to spectral anal} You may recognize by the spectrum of a 



-. not only the chemical nature of the gas, but you may also obtain 

 indications of its more intimate molecular structure (|iu'te a new 

 branch of science. Allow me now to select out of the results already 

 obtained two instances only. Let me try to give what I may call the 

 history of the spectra of two elementary bodies of sulphur and nitro- 

 gen. In order to analyze by the prism the beautiful light produced 

 by the electric current, if it pass through a rarefied gas, I gave to the 

 tube in which the gas is included such a form that its middle part was 

 capillary. Thus I got within this part of the tube a brilliant film of 

 light, extremely fitted to be examined by the prism. After having 

 provided myself with apparatus more suited to my purposes, I a-ked, 

 about a year a2o, my friend, Prof. Ilittorf, of Munster, to join me in 

 taking up my former researches. The very first results we obtained 

 in operating on gases of a greater density opened to us an immense 

 field of new inve.-tigation. \Ve found that the very same elementary 

 substance may have two, even three, absolutely different spectra, 

 which only depend on temperature. In our experiments we made use 

 of Ruhmkorifs induction coil, whose discharge was sent through our 

 spectral tubes. In order to increase at other times the Heating power 

 of the discharge, we rnudc u_-e of a Leydenjar. Kow, let us suppose a 

 bpecaral tube, most highly exhausted by Geissler's mercury pump, con- 



