Telescopes—Life of Fraunhofer. 309 
trum. In these experiments, he discovered in the orange 
compartment of the spectrum, produced by the light of the 
fire, a bright line, which he afterwards found to exist in all 
spectra, and by means of which he was enabled to determine 
the refractive powers of the bodies which produced them. 
By using prisms entirely exempt from veins,—by carefully 
excludmg 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 
nuiiber of black lines ‘parallel to one another, and perpen- 
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 different spectra afforded precise measures of the 
action of the prism on the rays which formed the correspon- 
ditig colored spaces. The valuable Memoir in which these 
discoveries are consigned, was published in the fifth volume 
of the Memoirs of the Academy of Munich for 1814 and 
1815, and also in a separate pamphlet entitled Bestimmung 
des Brechungs, und Farbenzerstreuungs, Vernogens ver- 
schiedener 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 Encyclopaedia. — ' Bi. 
About this time, in 1817, Fraunhofer was elected a mem- 
ber of the Academy of Bavaria, of which he was an active 
supporter. i ne ees ce ue 
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 of Neue 
Modefikation des Lichtes durch gegenseilige Hinwirkung 
und Beugung der Strahlen und gesetze derselben. In these 
éxperiments, of which we have given.a full account in the 
article Optics 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 
_* Above twenty years ago, lines were discovered in the spectrum by Dr. 
Wollaston. See Phil. Trans. 1802. : 
