NATURAL PHILOSOPHY. 171 



of metal existing in light, and the probability of certain dark lines in 

 the solar spectrum being formed by iron ! " Thus, the fact of the 

 existence of iron in the body of the sun, at a distance of ninety-five 

 million of miles, is represented by these scientific fanatics we really 

 can use no milder term as being identical with the existence of iron 

 in the sunlight, which, travelling at the rate of one hundred and 

 ninety-two thousand miles per second, bathes the whole universe in 

 its vivifying beams. 



Of stellar chemistry applied to other self-luminous celestial bodies, 

 we have at present but little knowledge. Fraunhofer, as we have 

 already stated, observed that the spectra of the fixed stars contained 

 dark lines differing from those seen in the solar spectrum. The half- 

 century which has elapsed since Fraunhofer made these observations 

 has not brought us further knowledge on this point, although it has 

 assured us of the truth of his statements. In the spectrum of Sirius 

 he observed no dark lines in the orange-colored region ; but in the 

 green there was a distinct line, and in the blue two dark bands, none 

 of which were seen in solar light. The spectra of other stars were 

 likewise examined by Fraunhofer, and they appeared each to differ 

 from the other. The difficulties attending the exact observation and 

 measurement of the dark lines in the spectra of the stars are, of 

 course, very great ; but, with the aid of the vastly improved optical 

 instruments of the present day, we believe that astronomers will 

 overcome these difficulties ; and we look forward with interest to no 

 far distant time when we shall receive some clue to the cause of the 

 color of those wonderful blue and red stars which appear to be con- 

 fined to certain quarters of the heavens. 1 



In the last chapter of Professor KirchhofF's Memoir he puts for- 

 ward a theory on the physical condition of the sun. Doubtless the 

 professor is as well aware as any one can be of the great difference 

 between his discovery of the existence of the metals in the sun and 

 his physical theory of the solar constitution. One is an ascertained 

 fact, the other is a mere hypothesis. It is, however, necessary to point 

 out this difference, lest many who may not agree with the theory of 

 the physical constitution of the sun proposed by KirchhofF should 

 think themselves at liberty to discard his discovery of the presence of 

 the metals in the solar atmosphere. It is not possible here, however, 

 to do more than quote one or two passages from his Memoir, to give 

 an idea of his views respecting the structure of the sun : 



" In order to explain," he says, " the occurrence of the dark lines 

 in the solar spectrum, we must assume that the solar atmosphere en- 

 closes a luminous nucleus, producing a continuous spectrum, the 

 brightness of which exceeds a certain limit. The most probable sup- 

 position which can be made respecting the sun's constitution is, that 

 it consists of a solid or liquid nucleus, heated to a temperature of the 

 brightest whiteness, surrounded by an atmosphere of somewhat lower 

 temperature. This supposition is in accordance with Laplace's cele- 

 brated nebular theory respecting the formation of our planetary sys- 

 tem. If the matter, now concentrated in the several heavenly 



1 An examination of the spectra of the fixed stars has already been entered upon 

 by Professor Airy, of the Royal Observatory of England. 



