26 
fy L(0H8), eS, 
ue 
oth’ 29-f d-9-f" 
ie iy a itt, oa 
sn Gey) ene 
The condition of distinct vision gives V= z+ 2, whence is 
derived 
, Bo aE Fb ox vy 
: Sp eae eae — 2 —: 
26=d +f - (a >) or nearly =f" +f’ + op 
using which in 2, and setting 2a for x, we have 
d” — 60a*d' = 120a‘, 
Equating the value of d’ given by this to its general one, we 
have 
Si —- 3) + 60°790a?— 0°63151a' + 0°43461a4 — 0°29979a'+ Ke. 
A 
ea F+ 5 
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. 
JS = 6°68. 
f= 1°35. M = 240. 
d=5-4l. @ =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. 
