Sc eafrcmt eae ees of Microscopie Objectives. 155 
TABLE—continued. 
No. Name of Maker. A. 1. Focal Length. B. Diff. A. |Diff. B. 
mm. mm. in. in, in. 
c 31 Dry .. | 250 | 1-696 | -0668 Ps 0005 
d 90.) "a6! err 31 Wet .. | 250 | 1°689 | °0665 3 Oc “0006 
13 | Smith & Beck, + in. ae 259 | 4°906 | +1931 | -2000 |—-0069 |-0017 
14a| Smith & Beck, £ in. 0 253 | 5°332 | °2099 | *2500 |—°0401 |-0006 
b SHES ee 18 253 | 5°038 | +1983 | .. as 0005 
15 | Smith & Beck, 2 in. ye 257 16°330 | °6429 | 6667 |—-0238 |-0000 
16* | Smith & Beck,14in. | Singlelens | 276 33-990 |1°3382 1°5000 _—*1617 |:00383 
17a) Collins, 54 in. 3 208°) S180) [P3220 },.)) il) 0009 
b ao.) “Abe staee 20 259 | 8°502 | -3347 | -4000 —-0653 |-0010 
18* | Collins, 13 in. Se 271 |42°572 |1°6761 |1-5000 |4+°1761 |-0047 
19a| Spenser, 3 in. Unced 266 | 9°717 | °3826 | *5000 |—-1174 |-0000 
b i Poeyeee Cov’d ZOG8 |S? OL7 \peaoera ie x. a ‘0018 
ee 
20a foe aoe ay 0 Dry .. | 258 | 2+286 | -0899 | -0833 +-0066 |-0002 
Eo OF 
b eae 19 Dry 257 | 1°620 | -0638 “0004 
ce 6°3 Dry 296 | 2°024 | :0797 oe OF *0012 
d Bee figs 6°3 Wet 256 | 1:995 | -0786 | -0667 |+°0119 |-0003 
21 |) Rolles; in. 0 Dry . 257 | 2°213 | -0871 | -0833 |+-0038 |-0011 
22 | Tolles, 3, in. 0 Dry . 257 | 2°898 | -1141 | -1000 |+-0141 |-0014 
23a) Tolles, 5 in. 0 Dry 258 | 2°874 | -1131 | -1000 |+-°0131 |-0000 
b age 14 Dry 259 | 2-283 | -0s99 | .. .. {0008 
ce AC 0 Wet 258 | 2°910 | -1146 | -1000 |+-0146 |-0005 
d so col Sac 14 Wet 259 | 2-263 | :0891 2 a “0004 
24a Tolles,iin. .. Ohta 258 | 3°217 | +1267 | +1250 |+°0017 |-0011 
b AG 46 Ho ec 163. 258 | 2°683 | -1056 ae Be *0005 
25a! Tolles, din. .. ORS, 263 | 6°083 | *2395 | +2500 |—-+0105 |-0011 
b SE EE 10%; 263 | 5°675 | -2234) .. ss 0026 
26 | Tolles, + in., 2nd Q. 246 | 6:143 | +2418 | +2500 |—-0082 |-0009 
27 | Tolles, +in., 2nd Q. 20 248 | 6:400 | -2520 | -2500 |+--0020 |-0010 
28* | Tolles, 1in., 2nd Q. | Singlelens | 259 25-188 | -9916 |1°0000 |—-0084 |-0000 
29a| Wales, =, in. Ones 258 | 6°818 | -2684 | -4000 |—*1316 |-0008 
: po. poh ac he 258 | 6°563 | -2584 oc bc *0007 
30 | Zentmayer, 4 in... 255 | 9-193 | °3619 | -4000 |—-0381 |-0009 
31* | Zentmayer, 58, in... 269 |20°113 | -7918 | -8000 |—-0082 |-0000 
32* | Zentmayer, 13 in... 50 280 |36°839 |1°4504 |1°5000 |—-0496 |-0022 
33.a| Grunow, + in. Une’d 273 | 5:253 | -2068 | +2500 |— +0432 |-0012 
b} bo Go ae Cov'd 273 | 5°059 | -1992 Ee o6 *0003 
34 | Grunow, 3 in. nin 255 | 8-902 | -3505 | -5000 |—*1495 |-0021 
The contents of column A may need some further explanation. 
The immersion lenses were measured both wet and dry to deter- 
mine the change of focal distance, which is very small unless the 
interior arrangement of the lenses is altered by moving the index 
circle. The figures in this column are the numbers given by the 
index if there was one; if no index was attached to the objective 
the extremes of the adjustment were taken, and are indicated by the 
words “ Unc.” for uncovered, and “ Cov’d” for covered adjustment. 
The +4, millimetre scale used as the object was always uncovered, 
whether the lens was adjusted for covered and uncovered objects, as 
no other method seemed so generally applicable. This, of course, 
rendered the definition somewhat indistinct when the lens was 
