THE MICROSCOPE. 
is a tabulated statement of the powers resulting from these com¬ 
binations, the four eye-glasses being designated in the order of 
tbeir powers, by the letters A, b, c, and d. The prices of the 
object-glasses severally are given in the last column of the table, 
and the slightest reference to them will explain the general desire 
of microscopists to diminish expense, by varying their powers, by 
the expedient of separating the lenses which enter into the com¬ 
position of the object-pieces. 
Achromatic Object-glasses for Microscopes. 
Object-glasses. 
Angular 
Aperture. 
Magnifying Powers with the 
various Eye-glasses. 
I 
! 
Price. 
' 
A. 
B. 
C. 
D. 
£ 
s. 
d . 
2 
inches . . 
12 
degrees. 
20 
30 
40 
60 
3 
0 
0 
I 
n • • 
15 
11 
60 
80 
100 
120 
2 
0 
0 
I 
n • • 
22 
11 
11 
11 
11 
11 
3 
10 
0 
\ 
ii • • 
65 
11 
100 
130 
180 
220 
5 
5 
0 
i 
ii • • 
85 
11 
220 
35 o 
500 
620 
5 
5 
0 
i 
ii • • 
135 
11 
320 
510 
700 
910 
10 
0 
0 
i 
8 
ii • • 
150 
11 
420 
670 
900 
1200 
12 
0 
0 
tV 
n • • 
170 
t 11 • 
650 
900 
1250 
2000 
18 
o- 
0 
When angular apertures, so extreme as those indicated in the 
preceding table, are attempted, it is necessary that the object- 
lens presented to the pencil diverging from the object, shall be 
of the meniscus form, the concave side being turned towards the 
object, for the reasons explained in 19. 
Besides the larger class of instruments above described, Mr. 
Ross constructs microscopes in a variety of other forms, which 
are placed within the reach of those who do not find it conve¬ 
nient to incur the expense of the larger instrument. 
MESSES. SMITH AND BECK’S MICEOSCOPE. 
84. The largest and most efficient class of instruments con¬ 
structed by these artists, do not differ much in their mounting 
from those of Mr. Ross above described. Like the latter, they 
are supported by a horizontal axis, between two strong vertical 
pillars, screwed into a tripod base. The instrument with its 
appendages, turning on the horizontal axis, can thus be placed at 
any obliquity whatever with the vertical. The coarse adjust¬ 
ment of this microscope is made by a rack and pinion, by which 
82 
