251 



F F f 



V f+ V 



and it must therefore be increased by these two terms, of which, 

 however, the last is unimportant. The power with the eye 

 alone is, therefore, to be added to that given by the eye-piece. 

 In Lord Rosse's telescope F = 54 feet, and, therefore, this 

 addition is 108, quite sufficient to separate pretty close double 

 stars. In the Armagh reflector, which is of Cassegrain's con- 

 struction, it is even greater, being 138 with the highest con- 

 vex mirror of 12 inches focus. 



The Academy then adjourned to Wednesday, the 25th 

 February, 1852, at 4 o'Clock, p.m. 



