1861.] on the Physical Basis of Solar Chemistry, 391 



capsule of carbon was filled with mercury, which formed the positive 

 electrode of the electric lamp ; a carbon point was brought down upon 

 this ; and on separating one from the other, a brilliant arc containing 

 the mercury in a volatilized condition passed between them. The 

 spectrum of this arc was not continuous like that from the solid carbon 

 points, but consisted of a series of vivid bands, each corresponding 

 in colour to that particular portion of the spectrum to which its rays 

 belonged. Copper gave its system of bands ; zinc gave its system ; 

 and brass, which is an alloy of copper and zinc, gave a splendid 

 spectrum made up of the bands belonging to both metals. 



Not only, however, when metals are united like zinc and copper 

 to form an alloy, is it possible to obtain the bands which belonged to 

 them. No matter how we may disguise the metal — allowing it to 

 unite with oxygen to form an oxide, and this again with an acid to 

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

 belonging to the metal reveal themselves with perfect definition. 

 Holes were drilled in a cylinder of retort carbon, and these being 

 filled with pure culinary salt, the carbon was made the positive elec- 

 trode of the lamp : the resultant spectrum showed the brilliant yellow 

 lines of the metal sodium. Similar experiments were made with the 

 chlorides of strontium, calcium, lithium,* and other metals ; each 

 salt gave the bands due to the metal. Different salts were then mixed 

 together, and rammed into the holes in the carbon ; a spectrum was 

 obtained which contained 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 inti- 

 mation ? 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. Wollaston, were 

 investigated with profound skill by Fraunhofer, and named from him 

 Fraunhofer's lines. They have been long a standing puzzle to 

 philosophers. The bright lines which the metals give us have been 

 also known to us for years ; but the connection between both classes 



* The vividness of the colours of the lithium spectrum is extraordinary : it 

 contained a blue band of indescribable splendour. It was thought by many, 

 during the discourse, that I had mistaken strontium for lithium j as this blue baud 

 had never before been seen. I have obtained it many times since ; and my friend 

 Dr. Miller, having kindly analyzed the substance made use of, pronounces it 

 chloride of lithium. — J. T, 



