26 
aft: 2+ (7-4) opt — 9). 
“Us 
ott 29-f')” d-o-f’ 
,_ S(t -o+ me agg 2 Niet 
en) Ae =) ye 
The condition of distinct vision gives V= z+ 2, whence is 
derived 
W=d+f'-Y Fe fs fird; i 
$ i a y 
using which in 2, and setting 2a for z, we have 
a d? — 60a?d’ = 120a‘. 
Equating the value of d' given by this to its general one, we 
have 
G us 5)* + 60°790a?— 0°63151a° + 0:4346 1a‘ — 0:29979a> + &e. 
% A 
Bis) mee 
os 
With F = 9A = 36, this gives 
a = 0°7115 = 8:54 inches. 
f = 8-02. 
f= 1-423. M = 240. 
d = 6:40. @ = 13°88. 
d= 31:34. 
Distance of mirror = 29°60. 
With F = 8A = 32 we have 
a = 0°6760 = 8:11 inches. 
S = 6-68. 
ff = 1:35. M = 240. 
d=5-4l. 6 =13°88. 
d' = 28°30. 
Distance of mirror = 26°59. 
In these the field is as large as can be obtained with this power 
m any telescope without a triple eye-glass. 
