SECT. IT. 129 



SECTION IY. 



THE SOLAR SPECTRUM, SPECTRUM ANALYSIS, SPECTRA OF GASES AND 

 VOLATILIZED MATTER, INVERSION OF COLOURED LINES, CONSTITU- 

 TION OF SUN AND STARS. 



To the ' unrivalled genius of Sir Isaac Newton we 

 owe the solar spectrum, and the laws of coloured rings, 

 by aid of which, Dr. Thomas Young proved and estab- 

 lished the undulatory theory which forms the basis of 

 the whole science of light. The visible part of the 

 solar spectrum forming a band of seven colours was 

 supposed to be continuous till the year 1802, when Dr. 

 Wollaston looking with a prism whose axis was 

 parallel to a narrow slit in a window shutter, at a sun- 

 beam passing through it, discovered seven dark lines 

 crossing the coloured band, at right angles to its 

 length. 



Twelve years afterwards, Fraunhofer of Munich, a 

 celebrated optician, magnified the spectrum of a ver- 

 tical line of light passing through an upright prism by 

 receiving it upon the object glass of a telescope, and 

 discovered 600 dark lines. Having ascertained that 

 the position of the lines in the spectrum, and their dis-) 

 tances from one another, are invariable under every 

 circumstance, he determined their places accurately 

 and drew the diagram known as Fraunhofer's lines, 

 which is universally referred to as a standard of com- 

 parison. For that purpose, the principal lines are 

 designated by letters ; thus the dark line A is in the 



VOL. I. K 



