APPENDIX. 
175 
CONDENSERS. £ s. d. 
Zeiss Achromatic, N.A. 1, fig, 13 .. ... ... 3 I 5 0 
Abbe Illuminator, N.A. i'i ... ... ... ... 220 
Powell and Lealand Achromatic, N.A. 1, with fittings, 
fig. 14 ... ... ... ... ... ... 880 
Powell and Lealand Achromatic, N.A. 1*4, with fittings 
fig. 14. 15 1 5 
Watson’s Holoscopic Oil-immersion,with fittings complete 6 10 
An ordinary Achromatic Condenser with stops, about 160° 3 3 
Paralleliser, Nelson’s, fig. 21 . ... about 1 1 
o 
o 
o 
o 
OBJECTIVES. 
The most costly are the apochromatics of Zeiss ; 
next come the apochromatics of Powell and Lealand, 
and other makers ; next, the “ quasi-apochromatics ” of 
various makers, as Leitz, etc.; next come the better- 
class students’ glasses, e.g., oil-immersion objectives of 
high power and fair aperture; twelfths, by Swift, Beck, 
and others; N.A. about 1:3; prices about ^8 to £10; 
lastly, low-angled objectives, achromatic. Watson’s 
new “ Holoscopics ” cost—25 mm. £2 5s., 12 mm. 
£2 ios., 6 mm. £% 4 mm. £4. 
Powers being equal, prices vary with apertures, a 
large aperture glass costing more than a narrow aper¬ 
ture of the same focal length. 
£ 
s. 
d. 
Zeiss “ Planar,’ - 35 mm. ... ... . 
5 
0 
0 
„ ,, 75 and 100 mm. ... ... each 
6 
0 
0 
Watson’s “ Holoscopic,” 3 inches, and others... 
4 
0 
0 
ILLUMINATING APPARATUS. 
Oil Lamp, large wick, fig. 19 . 
3 
0 
0 
Swift’s Nelson-Dallinger Lamp, with double paralleliser, 
small wick 
2 
10 
0 
