128 SUMMARY OF CURRENT RESEARCHES RELATING TO 
(2) Substage Condenser (single lens), by Beck.— Flat upper face of 
lens taken as point of reference A. 
A = 251-8 
Z x = 356-32 ; Z 2 = 196-5 
-76-1 + 49-6 
F, = 280-22 F 2 = 246-1 
Z\ = 370-54 Z' 2 = 182-17 
f = mean of Z\ — Z x and Z 2 — Z' 2 = 14-28 mm. 
JF = 65- 4 dioptries. 
H„ = F ! - / = 265-94 
Ho = F 3 +/ = 260-38 
k = H x - H 1 = 5-56 mm. 
(3) Coddington Lens, reputed 1 in. focal length. — Summit of one 
curved face taken as point of reference. 
A = 265-8 
B = 280-9 
F l = 299-3; F 2 = 247-2 
Sj = 325-6; S 2 = 220-8 
/ = (mean of S x — F x and F 2 — S 2 ) = 26-35 
JF = 37 • 95 dioptries. 
H x = F t - f= 272-95 
H 2 = F 2 + f= 273-55 
k = Hj — H 2 = — 0-60 mm. 
The Gauss points are crossed, and close together. 
(4) Objective 1-in., by B. and J. Beck. 
A (front of lens) at 248 • 2. 
F 1 = 279-88 
F 2 = 241-98 
S x = 300-09 
S 2 -- 221-75 
/= 20-22 mm. 
JF = 49*46 dioptries. 
H l = 259-67 
H 2 = 262-21 
k = — H 2 = — 2-54 (Gauss points crossed). 
(5) Objective 1/4 in., by E. and J. Beck. — Back focus too deep in 
tube to use ordinary micrometer; used a l^-in. objective instead, as 
auxiliary lens, to explore focus. 
A ( front of lens) at 252 • 4 
Fj = 274-88 
F„ = 252-14 
S“ = 281-20 
S 2 = 246-2 
f — 6 • 13 mm. 
JF = 163-1 dioptries. 
Hj = 268-75 
H 2 = 258-27 
k = Hj — H 2 = 10-48 mm. 
