494 HISTORY OF SCIENCE. 



was it any wonder that the sages of old deemed the orbs of the starry 

 sphere to be eternal and incorruptible ? But from the time when the 

 telescope of the illustrious Florentine was pointed to the sky, men's 

 conceptions of the heavenly bodies began to undergo modifications. 

 When two of the greatest intellects of last century Laplace, the 

 French mathematician, and Kant, the German metaphysician had 

 simultaneously and independently conceived and propounded that 

 bold speculation called the Nebular Hypothesis, the scientific concep- 

 tion of the universe had taken a distinct form. This hypothesis had 

 its justification in the revelations which the improvement of the tele- 

 scope afforded of the configurations of the sun, moon, planets, and 

 nebulae. Astronomers have had reason to be gratified with the great 

 additions to our knowledge which the gigantic telescopes of Herschel 

 and the great refractors of more recent times have been making. 

 Yet it appeared as if all knowledge of the chemical nature of extra- 

 terrestrial matter was completely and hopelessly denied. There was, 

 indeed, the exception of the aerolites, those metallic masses which fall 

 upon the earth from the realms of space. The chemist could of course 

 take a fragment of an aerolite to his laboratory, analyse it into its 

 constituent parts, and state the name and quantity of each element it 

 contained. But could astronomer or chemist ever hope to find, with 

 the same certainty, what chemical elements exist in the far-distant sun ? 

 Kirchhoff and Bunsen not only developed spectroscopy as a method 

 of detecting with great ease, certainty, and delicacy the presence of 

 the various elements in substances which may be handled in the labo- 

 ratory, but the principle by which the former philosopher explained the 

 Fraunhofer lines laid the foundation for cosmical chemistry. Apply- 

 ing this principle to the sun, we can understand how the central 

 part of our luminary would of itself yield a continuous spectrum ; 

 but the substances surrounding it as vapours, and forming an in- 

 tensely heated atmosphere, intercept those radiations which they are 

 themselves capable of emitting. Thus, in the experiment already 

 mentioned the ignited lime would correspond with the solid or a liquid 

 nucleus of the sun, while the sodium-flame would represent the sodium 

 vapour contained in its atmosphere. Kirchhoff undertook the task 

 of comparing the positions of the Fraunhofer or dark solar lines with the 

 bright lines in the spark spectra of our several elements. In comparing 

 the very numerous bright lines yielded by the spark-spectrum of iron 

 with the Fraunhofer lines, he found that for every bright iron line 

 there was, occupying exactly the same place in the spectrum, a dark 

 Fraunhofer line. The coincidence in position was perfect for each 

 of several hundred lines, and not only so, but the relative intensities 

 and widths of the lines in the two spectra corresponded, line by line. 

 Kirchhoff prepared with great care a map of the solar spectrum, in 

 which the positions and intensities of many hundred lines were laid 

 down. To those solar lines which he found identical with lines of one 



