Explanation of the 3 Classes of Achromatic Microscopes,
Mannfactnred by Smith and Beck.
A C om p o u n d A ch rom atic Mic roscope c o n sists, essen tia lly , o f a n O b jec
t-G la s s , a n d a n E y e -p i e c e ; so called, b ecau se th e y ‘‘''e
n e a r th e o b jec t an d th e eye w h en th e I n s trum e n t is in u s e . 1 h e O b je c t
Glass screws, a n d th e E y e -p ie c e slides, in to o p p o s ite en d s o f a tu b e
te rm e d th e Body, an d u p o n th e u n io n o f th e two th e M ag n ify in g Power
d ep en d s B u t some f o iL o f S ta n d is in v ariab ly emp oyed to c a rry th e
M a g n ify in g Power, to h o ld , o r to give tra v e rs e to th e ob ject, an d to
receive various a p p a ra tu s fo r I llumin a tio n .
U n d e r th is g en e ra l d escrip tio n th e following Mic roscopes may h e a r r
a n g e d in Three Classes
I n th e F ir s t, th e M a g n ify in g Power, tb e S ta n d , an d th e Illum in a tio n
a re c a rried to th e g r e a te s t po ssib le p e rfe c tio n .
I n th e Second, th e same M a g n ify in g P ow er is c omh in ed w ith a
S ta n d , a n d a p p a ra tu s fo r Illum in a tio n , less expensive b u t v e ry eiiicient.
I n th e T h ird , th e cap ah ilitie s o f a ll th e pai;ts a re lim ited , h u t y e t
e q u a l to th e req u irem e n ts o f m an y , a n d o f co n sid e rab ly less co st.
A l th o u ih th e following L is ts o f A p p a ra tu s a re com p le te in e a ch Class,
a n y p o r tio n o f th em c an b e o rd ered , a n d th e S ta n d s are n o t r eq u ired by
t h e m ak e rs fo r su b s eq u e n t a d d itio n s.
ACHROMATIC OBJECT-GLASSES^.
For the 1st & 2nd Class Stands (Nos. 1, 2, 3 & 4).
T h e in crease o f th e an g le o f a p e rtu re o f th e O b je c t-G la sse s in th e
following T a b le is m o re especially wo rth y o f n o tic e in th e lower powers,
which, a d ju s tin g th ro u g h considerable th ic k n e s s o f glass, o r some d ep th
in to w a te r, will, w ith a larg e a p e rtu re , e x h ib it th o se ob jects which are
th e m o st fre q u e n tly ex am in ed by th e n a tu ra lis t, with a defin itio n th a t
a sm a lle r an g le o f a p e rtu re c a n n o t give. O n e o f th e s e Ob ject-Glasses,
a 4 - 1 0 th s (erro n eo u sly called “ h a lf-in c h ” ), is th u s a llu d ed to iu th e
“ R e p o rts o f th e Ju rie s o f th e G re a t E x h ib itio n ” (p. 2 6 6 ), Class X .,
N o . 253.
“ T h e h a lf-in c h focus o f 70° a p e rtu re is a wo n d erfu lly fine c om b in a tio
n , easily sh owing o b jec ts co n sid ered difficult for a o n e -e ig h th
in ch fo cal le n g th a little m o re th a n a y e a r since, an d b e a rin g
th e ap p lic a tio n o f th e h ig h e r eye-pieces in an u n p re c e d e n te d
m an n e r.”
Focal
length.
Linear Magnifying Powei
With
N«.l
r nearl;
Eye-I
NO. 2
7-
’ieces.
No. 3
Angle of
aperture
about
Price.
Lieberkuhn
additional.
1 inch
Draw-tube closed
Add for each inch
of tube drawn out
20
4
45
6
80
8
13 degrees
£ . S . d .
3 0 0 15s.
f i n c h
, Tube closed ........
Add for each inch
of tu b e .................
60
7
105
12
180
20
27 degrees 3 3 0 11s.
A t “ ch
Ditto
Ditto
Tube closed ........
Add for each inch
of tu b e .................
Ditto
Ditto
120
12
do.
do.
210
20
do.
do.
350
35
do.
do.
55 degrees
65 degrees
75 degrees
5 5 0
6 6 0
7 7 0
10s.
10s.
10s.
-g- inch
Ditto
Tube closed ........
Add for each inch
of tu b e .................
Ditto
240
30
do.
430
45
do.
720
. 80
do.
85 degrees
100 degrees
6 6 0
7 7 0
-g- inch
Tube closed ........
Add for each inch
of tu b e .................
450
40
760
60
1300
115
120 degrees 10 10 0
T h e E r e c tin g Glass fo r low p ow e r ....................................................... ,^:'l 0 0
T h e m ag n ify in g power o f th is glass with th e 2 -3 rd s O b je c t-G la ss
an d employing eye-pieces No s. 1 & 2 , is from 5 to 150.
* These Object-Glasses can be adapted to Ross’ or Powell and Lealand’s
Microscopes without the instruments being required for th a t purpose.