Telescopes — Life of Fraunhofer. 309 



trum. In these experiments, he discovered in the orange 

 compartment of the spectrum, produced by the liojit of the 

 fire, a bright iine, which he afterwards found to exist in al! 

 spectra, and b}' means of which he was enabled to determine 

 the refractive powers of the bodies wdiich produced them. 



By using prisms entirely exempt from veins, — by carefully 

 excluding all extraneous light, and even stopping those rays 

 which formed the colored spaces that he wished to examine, 

 he discovered that the spectrum was intersected by a great 

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

 dicular to its length.* In the spectra formed by ail solid and 

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

 he has reckoned five hundred and ninety in all,) but he found 

 that they had fixed positions, and that the distances between 

 them in diflerent spectra atl'orded precise measures of the 

 action of the prism on the rays which formed the correspon- 

 ding colored spaces. The valuable Memoir in which these 

 discoveries are consigned, was published in the fifth volume 

 of the Memoirs of the Academe/ of Munich for 1814 and 

 1813, and also in a separate pamphlet entitled Bcstimmung 

 des Brechimgs^ und Farhenzerstreimngs^ Vermogcns ver- 

 schiedener Glasarten. The writer of this notice fiad the 

 satisfaction of first translating this memoir into English, and 

 of publishing an abstract of its results in the article Optics 

 in the Edinburgh Encyclopaedia. 



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 

 complete series of experiments on the inflexion of light. 

 These experiments he published in the eighth volume of the 

 Memoirs of the Academy of Munich, under the title o^ Neue 

 Modefikation des Lichtes durch gegenseilige Eirnvirkiing 

 und Beugung der Stralden und gcsetze derselhen. In these 

 experiments, of which we have given a full account in the 

 article Optics in the Edinburgh Encyclopaedia, Fraunhofer 

 employed a heliostate forgiving a fixed direction to the solar 

 ray, and he examined all the phenomena through a telescope 



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

 Wollaston. See Phil. Trans. 1802. 



