Telescopes — Life of Fraunhofer. S07 



1805, M. Utzschneider constructed furnaces for carrying 

 on the experiments upon a well organized plan. The first 

 attempt created much expense, on account of the repeat- 

 ed experiments which it required, but it nevertheless fur- 

 nished several good pieces of both kinds of glass. The 

 optician, Riggl, polished the first lenses in 180G and 1807. 

 At this period Fraunhofer found himself in a very critical 

 situation. Professor Schiegg always encouraged him to go 

 to M. Utzschneider, but Fraunhofer was long in resolving to 

 do this, believing that the latter had forgotten him, and 

 knowing that he was well satisfied with his own optician. 



M. Utzschneider received Fraunhofer in a very friendly 

 manner, and after a short conversation, it was agreed that 

 he should also become an optician in the establishment. 

 Fraunhofer was then employed to calculate and polish len- 

 ses of considerable dimensions which came from the furna- 

 ces of Benedictbauern. These lenses were destined for the 

 instruments of the observatory of Buda. It was afterwards 

 agreed to transfer all the optical part of the establishment 

 to Benedictbauern, and to give the complete direction of it 

 to Fraunhofer. Our philosopher had already studied catop- 

 trics, and had even written a Memoir on the aberration 

 which takes place without the axis in reflecting telescopes. 

 He showed that hyperbolic mirrors are preferable to para- 

 bolic ones, and he also communicated the invention of a 

 machine for polishing hyperbolic surfaces. He now, howev- 

 er, resolved to give up this branch of the subject, as his time 

 was fully occupied in the preparation of lenses. 



One of the most difiicult problems in practical optics is 

 to give to spherical surfaces the last polish with that degree 

 of exactness which theory requires, because this final opera- 

 tion destroys in part that form which had been previously 

 given to the surfaces. M. Fraunhofer succeeded in remedy- 

 ing this evil by a machine which not only did not injure the 

 fine surface obtained by grinding, but which actually correc- 

 ted the inegularities committed in the first operation. It has 

 also the advantage of making the result independent of the 

 skill of the workman. 



In examining the glass which he used in reference to the 

 undulations and striae which it contains, he found that, in 

 the flint glass manufactured at Benedictbauern, there was 

 often not a single piece free of those irregularities which dis- 

 perse and refract the light falsely. Pieces of the same melt- 

 jng had not even the same refracting power, and this was 



