PHYSICAL BASIS OF SOLAR CHEMISTRY. 387 



perfect definition. Into holes drilled in a cylinder of 

 retort carbon, pure culinary salt is introduced. When 

 the carbon is made the positive electrode of the 

 lamp, the resultant spectrum shows the brilliant yellow 

 lines of the metal sodium. Similar experiments made 

 with the chlorides of strontium, calcium, lithium, 1 and 

 other metals, give the bands due to the respective 

 metals. When different salts are mixed together, and 

 rammed into holes in the carbon ; a spectrum is ob- 

 tained which contains the bands of them all. 



The position of these bright bands never varies, and 

 each metal has its own system. Hence the competent 

 observer can infer from the bands of the spectrum the 

 metals which produce it. It is a language addressed to 

 the eye instead of the ear ; and the certainty would not 

 be augmented if each metal possessed the power of 

 audibly calling out, ' I am here ! ' Nor is this language 

 affected by distance. If we find that the sun or the 

 stars give us the bands of our terrestrial metals, it is a 

 declaration on the part of these orbs that such metals 

 enter into their composition. Does the sun give us any 

 such intimation ? Does the solar spectrum exhibit bright 

 lines which we might compare with those produced by 

 our terrestrial metals, and prove either their identity 

 or difference ? No. The solar spectrum, when closely 

 examined, gives us a multitude of fine dark lines instead 

 of bright ones. They were first noticed by Dr. Wollas- 

 ton, but were multiplied and investigated with profound 

 skill by Fraunhofer, and named after him Fraunhofer's 



1 The vividness of the colours of the lithium spectrum is extra- 

 ordinary; the spectrum, moreover, contained a blue band of in- 

 describable splendour. It was thought by many, during the 

 discourse, that I had mistaken strontium for lithium, as this blue 

 band had never before been seen. I have obtained it many times 

 eince ; and my friend Dr. Miller, having kindly analysed the sub- 

 stance made use of, pronounces it pure chloride of lithium. J. T. 



c c 2 



