OPTICS. 271 



object under an angle not exceeding half a minute of 

 a degree. 



Sir William HerscheVs Telescope. 



The speculum of Sir William Herschel's 45 feet 

 telescope was 49J inches in diameter, 3J inches in 

 thickness, and weighed, when newly cast, 2118 

 pounds. It magnified 6450 times, and was com- 

 pleted on the 27th August, 1/89. 



