168 
Transactions of the Society. 
rs= — • 6757 ; s — r -4- (fi — 1 ) g = 1 * 6823 = h ; 
- 1 )h = 1 • 0434 = h ; p = = *03016; 
q = = - -03016; f= T 4= ~ *6476. 
d = *1731; 
/" + /_ d = *0486; 
<#> = 
df= - *1121 ; /"/ = - *563; 
Q = 7 “ -0486 = 2 + 2-307 ; 
•0486 
ttt = - 11-584. 
D = - 2-1339; 
D/' = - 1*855; cj>f=- 10-07; 
<£+/' - D = - 8*581; 
Q' = ?'-^Si = ?'- ,2162 > 
F = 
- 10*07 
- 8-581 
1-174. 
Working distance = *8135 
Magnifying power = 7*52 
We may here notice that owing to the greater thickness of this 
lens its true focus differs more from its nominal focus than the focus 
of the Stenheil did in Example 11. Its magnifying power for this 
reason is also less, being 7 * 5. 
Loups are often found to possess less power than they are 
stated to have, the power being calculated on the nominal, instead of 
on the true focus. 
Before passing on we must complete our examination of the Gauss 
method by considering the cases when one of the surfaces is plane. 
In a plano-convex or plano-concave lens, when r = oo , h = co , 
■p = g = - and q = 0. This means that p lies within the lens at a 
distance of - from the plane surface, and q is at the vertex of s ; the 
focus / = 
— s 
IM- 1 
Turning the lens round, we have s = co 
t 
p is at the vertex of r. 
q = — , and / = 
We now come to the consideration of the various forms that can 
be given to the achromatic doublet represented in Case 2 (fig. 15). 
