222 ANXTAL OF SCIENTIFIC DISCOVERT. 



upon the ol)joct-glass of the first tc]os^opo, and its rnys nro ron- 

 (It'ivd i)ar:ill('l ; it then passes throu^^li tlu" prism, is rt'lVactorl and 

 dfcnmj)osiHl, and ontcrstho second tcloscope, wiience it lalN upon 

 the eye. Any Uame may be put opposite the slit, and its jneiiliar- 

 ities examined, or, by the aid of a rellector, the sunli<i^iit may be 

 oast on part of the slit, so that we can see a solar spectrum along- 

 side of the tlame spectrum. Or, we may have the spectra of the 

 two llames at once, and compare them. The third telescope 

 carries a scale. 



The use of a spectroscope merely involves placinp^ the substance 

 to be examined in a spirit or <;as llame, an<l then lookinjj throu^^h 

 the telescope to examine the spectrum. Tiie number, position, 

 and color of the transverse lines are always the same from the 

 same sul)stance. A jx-rson soon Ijccomes experienced enough to 

 state in a moment wliat bodies are present. 



Understanding^, then, that various elementary bodies, when 

 volatilized in a llame and examined l>y :v spectroscope, give spec- 

 tra distingui>hi'd by l)rii;iit-eolored lines, soda by yellow, strontia 

 by red. etc., the reader is ready to grasp the next idea in the 

 investigation. 



If the light coming from such a source as a mass of white-hot 

 iron, wliieii is free tVom all Fraunliofer lines, be pas.sed througii a 

 llame wlicre soda is volatilizing, belore it is analjzed b}' tiie prism, 

 instead of seeing the l)right yellow lines characteristic of the soda, 

 we shall fmd in thi'ir place two dark lines. In other words, the 

 soda llame has interfered with the continuity of the spectrum of 

 the wiiiti'-iiot I)ody, and produced therein two Fraunliofer lines. 

 If a number of substances are burning in the llame at once, we 

 shall get in the spectrum an increased number of lines. A flame 

 refuses to permit the passage of rays of the same kind as it emits. 

 "White light passing tlirough a soda flame has the 3'ellow rays 

 sifted out of it. 



It is obvious at once, from such considerations, that we can 

 ascertain the constitution of the sun, both as regards his physical 

 character and chemical composition. From the fact that the lines 

 in his spectrum are dark, we infer that he has an intensely hot 

 solid or fluid nucleus, emitting light, and suiTounded by an atmos- 

 phere of flame in which there are many volatilized bodies. If he 

 were solely an ignited gas or flame, the lines of his spectrum 

 would be bright instead of dark. 



As regards chemical composition, it is only necessary to ascer- 

 tain what elementary substance can produce lines corresponding 

 to those in tlie solar spectrum. We can then at once be sure that 

 those bodies exist in the luminary. The presence of iron, 

 sodium, and a variety of other materials familiar to us here, has 

 thus been proved. 



The reader will at once perceive what an important bearing 

 these facts have on the construction and unity of the solar system. 

 We have shown that on two members of it — the sun and the 

 earth — the same substances are found, and we may, therefore, 

 infer that all the rest are similarly composed — for no other two, 

 at first sight, seem more unlike. The sun, and all his attending 



