310 Telescopes — Life of Fraunhofer. 



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 magnifying power from 30 to 110. The he- 

 liostate was placed thirty eight feet seven and a half inches 

 French measure from the centre of the theodolite. The di- 

 ameters of the apertures were measured by a micrometer 

 microscope, wJiich showed distinctly the two hundred thou- 

 sandth part of an inch., and sometimes even half that quan- 

 tity. All the ph.enomena which he thus observed and meas- 

 ured, he considered to be perfectly explicable on the undula- 

 ting system, with certain modifications ; and upon these prin- 

 ciples, he afterwards constructed a general analytical formu- 

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

 it followed that these phenomena would be modified in a 

 manner not only singular, but apparently extremely compli- 

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

 that eight thousand of them were contained in one inch. 

 After another set of experiments, he invented a machine, by 

 means of which he could construct these systems of lines 

 with that accuracy which the theory required. The de- 

 tails 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 

 Ahhandlungen ^ 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 labors as an optician. His 

 minor inventions are a new Heliometer a repeating loire Mi- 

 crometer., and an improved anmdar Micrometer. The prin- 

 cipal instruments which he has made, are the great parallac- 

 tic telescope, constructed for the observatory of Dorpat, and 

 of which we have given a fiill description and a drawing in 

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

 strument was L. 950. Its aperture is nine inches, and its fo- 

 cal length 13i feet. His next great work was another achro- 

 matic telescope, ordered by the King of Bavaria, and which 

 has an object-glass twelve incites in diameter, and eight feet 

 in focal length, but it is not yet ^completed. Although en- 



