SCIENTIFIC NE"^*. 335 



tained, Mr. Laknde has sought in his long experience 

 for facts which might answer that purpose. He has re- 

 marked, that at that time the use of the telescope of 

 verification (lunette d'epreuve^ was entirely unknown. —because the 



This yery commodious and simple instrument, which telescope of 

 •' 1 venfication 



might be supposed of as early an invention as the applica- -v^as not then 



tion of telescopes to sectors and quadrants, is more known, 

 modern than might be imagined. ^We possess the advan- 

 tage of this, as well as of many other articles of daily use, 

 without inquiring, after their inventors. It is mentioned 

 for the first time in the edition of Lalande's Astronomy, 

 of 176 4. In order to verify the parallelism of telescopes, 

 Bouguer adopted the use of two pins or studs, which were 

 mutually to be changed in place, in order to ascertain 

 whether they had really the same height. He himself 

 made use of a more imperfect method, w hich is still less 

 entitled than the studs to be put In competition with the 

 proof telescope of Lalande, which is at present universally 

 adopted. We do not know whether Graham had some 

 equivalent method of approximation to verify his sector. 

 Maupertuis makes no mention of any such thing in the 

 chapter wherein he treats of the verification of that in* ~ 

 fitrument, and this neglect may in part explain the error 

 "ivhich is imputed to him. 



Mr. Legciidre has been busied upon a question of im- Spherpldal tsx- 

 portance, though of rare application. His memoir is angles treated 

 entitled, '^ Analysis of Triangles traced on the Spheroid." ^y ^-^gendrc^ 



The early astronomers who measured the earth with 

 some exactness, considered it as a sphere of immense ra- 

 dius, in comparison with the small intervals they proposed 

 to ascertain. The greatest side of any triangle in these 

 operations does not exceed 60,000 metres, and the differ- 

 ence between such an arc and the right line that would 

 (connect its extremities, is scarcely two decimeters, or 

 the three hundred thousandth part. It was therefore, 

 with reason, supposed that triangles of so minute a cur- 

 ■^ature might be considered as right lined. 



In the latter operations wherein it was sought to de- 

 termine more exactly the difference between the teri^es- 

 trial globe and a perfect sphere, an attention to accuracy 

 was carried fartlier. The triangles formod at the surface 



• of 



