PHYSICAL BASIS OF SOLAR CHEMISTRY. 335 



form a salt; if the heat applied be sufficiently intense, 

 the bands belonging to the metal reveal themselves 

 with 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,* 

 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 com- 

 petent observer can infer from the bands of the spec- 

 trum the metals which produce it. It is a language 

 addressed to the eye instead of the ear; and the cer- 

 tainty 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 terres- 

 trial 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 com- 

 pare with those produced by our terrestrial metals, and 

 prove either their identity or difference? No. The 

 solar spectrum, when closely examined, gives us a multi- 

 tude of fine dark lines instead of bright ones. They 



* The vividness of the colours of the lithium spectrum is ex- 

 traordinary ; the spectrum, moreover, contained a blue band of 

 indescribable 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 

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

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



