THE MICROSCOPE. 89 
HARTNACK. ZeISs. SCHIEK. NACHET. 
No. Focal length. | No. Focallength. No. Focal length.| No. Focal length. 
1 2 A 1 1 2 0 2 
2 A 3 2 8 1 I 
3 3 B 3 3 : 2 : 
4 : C 4 4 1 3 l 
5 i ae ie a a ee b 
6 ; EK $ 6 i 5 4 
7 ; F eal en 4 6 a 
8 3 8 Tr 7 sig 
9 ae 9 ts 8 vp 
10! ts 10 ts) 9 vo 
il Sig 11 Saal ot 
12 a Ti ao 
13 = 12 ay 
14 am 
15 i 
16 ale 
17 ae 
18 a 
tained. On the other hand, the glass stage is as frequently in 
the way, and on the whole the student can very well dispense 
with it, as its disadvantages will nearly or quite counterbalance 
its convenience. No rubber should be employed around the 
stage nor in fact anywhere around the microscope.? ‘The 
1 Nos. to to 18 are immersion. 
2 Besides its electrical qualities which render it a nuisance, rubber is readily 
affected by turpentine and benzole which are so necessary in microscopic work. 
