THE MANUFACTURE OF TELESCOPES. 389 



satisfactory, and says that it readily shows the sixth 

 star in the trapezium of Orion, and the daily variations 

 in the colored portion of Mars. 



TELESCOPES BY ALYAN CLAEK, OF BOSTON. 



A little more than ten years since, Mr. Alvan Clark, 

 of Boston, undertook the manufacture of telescopes. His 

 first experiments were with reflectors, but being dissatis- 

 fied with these, he attempted the manufacture of object- 

 glasses. In 1846 and 1848, he made two object-glasses 

 of East Cambridge flint-glass. Between them he made a 

 telescope, of 5 inches aperture, of Gruinand glass which 

 was sold to Mr. "Welles, of Newburyport. This telescope 

 separated the close pair in the triple star Gamma Andro- 

 meda3, whose distance is two fifths of a second, and showed 

 the sixth star in the trapezium of Orion at intervals, 

 though with difficulty. After these, Mr. Clark made a 

 telescope of 4f inches aperture with which he discovered 

 three new double stars; and he has made in all more 

 than a dozen object-glasses exceeding four inches aper- 

 ture. The following is a list of the largest which he has 

 made: 



1. His largest object-glass is of eight inches aperture, 

 and now in the hands of Kev. "W. E. Dawes, of England, 

 unsold. It was sent to England in October, 1855, and 

 under date of December 20th, Mr. Dawes writes respect- 

 ing it as follows: " Its efficiency is certainly greater than 

 that of any other telescope I have tried, both in defining 

 the features of a planet, and in splitting close double 



