PHYSICAL BASIS OF SOLAR CHKMTSTRT. 255 
arc is not continuous like that of the solid carbon points, 
but consists of a series of vivid bands, each corresponding 
in color to that particular portion of the spectrum to which 
its rays belong. Copper gives its system of bands; zinc 
gives its system; and brass, which is an alloy of copper and 
zinc, gives a 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 belong 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 be- 
longing to the metal reveal themselves with perfect defi- 
nition. 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 obtained 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 bauds 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 com- 
position. Does the sun give us any such intimation? 
Does the solar spectrum exhibit bright lines which we 
* The vividness of the colors of the lithium spectrum is extraor- 
dinary; the spectrum, moreover, contained a blue band of indescrib- 
able splendor. 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 analyzed the substance made use of, 
pronounces it pure chloride of lithium. J. T. 
