Memoir of the Life of M. Fraunliofer, 7 



which formed the coloured spaces that he wished to examine, 

 he discovered that the spectrum was intersected by a greajt 

 number of black lines parallel to one another, and perpendi- 

 cular to its length.* In the spectra formed by all solid and 

 fluid bodies, he not only discovered the same lines, (of which 

 he has reckoned 590 in all,) but he found that they had fixed 

 positions, and that the distances between them in different 

 spectra afforded precise measures of the action of the prism 

 on the rays which formed the corresponding coloured spaces. 

 The valuable Memoir in which these discoveries are consign- 

 ed, was published in the fifth volume of the Memoirs of the 

 Academy of Munich for 1814 and 1815, and also in a sepa- 

 rate pamphlet entitled Bestimmung des Brechungs, und Far^ 

 benzerstreuungs, Vermogens verschiedener Glasarten. The 

 writer of this notice had the satisfaction of first translating 

 this memoir into English, and of publishing an abstract of its 

 results in the article Optics in the Edinburgh Encyclopedia. 



About this time, in 1817, Fraunhofer was elected a Mem- 

 ber of the Academy of Bavaria, of which he was an active 

 supporter. 



In speculating on the cause of the dark lines of the spec- 

 trum, our author was led to consider them as arising from the 

 interference of the rays, and he was induced to make a com- 

 plete series of experiments on the inflexion of light. These 

 experiments he published in the eighth volume of \he Memoirs 

 of the Academy of Munich, under the title of Neue Modefikon. 

 Hon des Lichtes durch gegenseilige Einwirlcung und Beugung 

 der Strahlen und gesetze derselben. In these experiments, 

 of which we have given a full account in the article Op- 

 tics in the Edinburgh Encyclopedia, Fraunhofer employed 

 a heliostate for giving a fixed direction to the solar ray, and 

 he examined all the phenomena through a telescope mounted 

 upon a large theodolite, by means of which he measured the 

 deviation of the inflected light. The object-glass was twenty 

 lines in diameter ; its focal length was 16.9 inches, and its mag- 

 nifying power from 30 to 110. The heliostate was placed 38 

 feet 7 1 inches French measure from the centre of the theodo- 



* Above twenty years ago, lines were discovered in the spectrum by Dr 

 Wollaston. See Phil. Trans. 1802. 



