8 'Memoir of the Life of M. Fraunhqfer. 



lite. The diameters of the apertures were measured by a 

 micrometer microscope, which showed distinctly the two hun^ 

 dred thousandth part of an inch, and sometimes even half 

 that quantity. All the phenomena which he thus observed 

 and measured, he considered to be perfectly explicable on the 

 undulating system, with certain modifications ; and upon these 

 principles, he afterwards constructed a general analytical for- 

 mula, to express these new laws of light. From this formula, 

 it followed that these phenomena would be modified in a man* 

 ner not only singular, but apparently extremely complicated, 

 if a number of parallel lines could be made so fine, that 8000 

 of them were contained in one inch. After another set of ex- 

 periments, he invented a machine, by means of which he 

 could construct these systems of lines with that accuracy which 

 the theory required. The details of these experiments were 

 read before the Academy of Munich on the 14th June 1823, 

 and will be found in this and the subsequent number of this 

 Journal. 



M. Fraunhofer likewise applied himself to the study of va- 

 rious atmospheric phenomena, such as halos, parhelia, &c, 

 which he published in Professor Shumacher'^s Astronomische 

 Abhandlungen, and of which we have given a notice in the last 

 number of this Journal, p. 348. 



Such is a brief sketch of the scientific researches of Fraun- 

 hofer, but, valuable though they be, they are in no respect 

 to be compared with his practical labours as an optician. 

 His minor inventions are a new Heliometer, a repeating 

 wire Micrometer, and an improved annular Micrometer. 

 The principal instruments which he has made, are the great 

 parallactic telescope, constructed for the observatory of Dor- 

 pat, and of which we have given a full description and a 

 drawing in No. iv. p. 306 of this Journal, The prime cost of 

 this instrument was L. 950. Its aperture is nine inches, and 

 its focal length 13 J feet. His next great work was another 

 achromatic telescope, ordered by the King of Bavaria, and 

 which has an object-glass twelve inches in diameter, and eight 

 feet in focal length, but it is not yet completed. Although 

 engaged in works of such magnitude, Fraunhofer was at the 

 same time carrying on others on a less scale, though not of 



