Chromatic Curves of Microscope Objectives. By E. M. Nelson. 17 
It is more than probable that of all objects photographically discovered, 
there is not one which cannot be visually demonstrated with a 
far lower power when the Microscope is critically used. 
Table of Resolving Powers in Lines to an Inch with 3/4 Cone of 
Direct Illumination. 
N.A. 
White Light. 
Between lines D and E 
46,666 waves per inch. 
Monochromatic Blue 
Light and Photography. 
Near line F 
53,333 waves per inch. 
0*1 
7,000 
8,000 
0-2 
14,000 
16,000 
03 
21,000 
24,000 
0*4 
28,000 
32,000 
0-5 
35,000 
40,000 
0-6 
42,000 
48,000 
0*7 
49,000 
56,000 
0-8 
56,000 
64,000 
0*9 
63,000 
10 
70,000 
The same as for 
1*1 
77,003 
white light. 
1*2 
84,000 
1*3 
91,000 
1*4 
98,000 
1-5 
105,000 
1*6 
112,000 
The above table agrees remarkably well with results actually 
obtained with the best lenses, and to show that this is so, the following 
table gives the actual resolutions made on diatoms in balsam with a 
3/4 cone from a Powell fluorite apochromatic condenser (1/4 of 
0*95 N.A.). 
Objective. 
O.I. 
N.A. 
White Light. 
Blue Light. 
Apochromatic 1 iD. .. 
28*9 
•32 
22,000 
25,000 
1. Achromatic 4/10 (1875) 
20-0 
•64 
40,000 strong 
49,000 
2. Apochromatic 1/2 
32*0 
•66 
46,000 
53,500 
3. Semi-apochromatic 1/4 
18-6 
•71 
53,500 
60,000 barely 
Achromatic 1/4 (1875) 
16*5 
•79 
53,000 barely 
60 , 000 barely 
Semi-apochromatic 1/7 
11*5 
•86 
60,000 
65,000 
4. Achromatic 1/5 .. 
16-3 
•88 
60,000 
65,000 barely 
Apochromatic 1/4 
23*2 
•95 
65,000 
— 
5. Semi-apochromatic 1/12 
9*7 
1-26 
90,000 barely 
— 
6. Apochromatic 1/8 
17-0 
1-43 
94,000 
1. Would resolve probably 42,000 with white light (construction same as achro- 
matic 1 /4, viz. triple front and baok, double middle). 
2. A very fine lens. 
3. A little more than 3/4 cone used ; this lens is a very strong resolver, and stands 
blue light even better than some apochromatics. 
4. A fine example of an achromatic by Gundlach. 
5. Will not resolve the Nitzschia curvula 90,000. 
6. Resolves Amphipleura pellucida 93,000-95,000. Less than 3/4 cone used. 
1893. 
c 
