C, a plane glafs, with a (mail piece o f black filk ftuck on i t ;
this glafs is to lay in a groove made in the ftage B.
M, a hollow glafs, to be laid occafionally on the ftage inftead
of the plane glafs C.
L, a pair of nippers. Thefe are fixed to the ftage by the pin
R ; the fteel wire of thefe nippers Aides backwards and forwards
in the focket, and this focket is moveable upwards and downwards
by means of the joint, fo that the pofition o f the objefi
may be varied at pleafure. The obje£t may be fixed in the nippers,
ftuck on the point, or affixed by a little gum water, &c.
to the ivory cylinder N.
O, a fmall pair o f forceps to take up fmall objects.
P, a brufh to clean the glaffes.
T o use E llis’s Microscope.
Take all the parts o f the apparatus out o f the b o x ; then begin
by fere wing the pillar A to the cover thereof; pafs the pin
R of the femicircle which carries the mirror through the hole
that'is near the bottom o f the pillar A j pufh the ftage into the
dove-tail at B, Aide the pin into thé pillar, (fee the N. B. above)
then pafs the bar E through the focket which is at the top of the
pin D, and ferew one of the magnifying lenfes into the ring at F.
The microfcope is now ready for ufe ; and though the enumeration
o f the articles may lead the reader to imagine the inftrument
to be o f a complex nature, we can fafely affirm, that he will find
it
it otherwife. The inftrument has this peculiar advantage, that
it is difficult to put any of the pieces in a place which is appropriated
to another..
Let the object be now placed either on the ftage or in the nippers
L, and in fuch manner, that it may be as nearly as pofiible
over the center o f the ftage : bring the fpeculum F over the part
you mean to obferve; then throw as much light on the fpeculum
as you can, by means of the mirror IL , and the double motion
o f which it is capable ; the light received on the fpeculum is reflected
by it on the objeft. The diftance of the lens E from the
objeft is regulated by moving the pin D up and down, until
a diftina view o f it is obtained. The rule which I obferve
is, to place the lens beyond it’s focal diftance from the objea,
and then gradually Aide it down, till the objedappears Aiarp and
well defined. The adjuftment of the lenfes to their focus, and
the diftribution of the light on the objea, are what require the
moft attention ; on the firft the diftinanefs of the vifion depends ;
the pleafure arifing from a clear view of the parts under obferva-
tion, is due to the modification of the light. No precife rule can
be given for attaining accurately thefe points; it is from pradice
alone that ready habits of obtaining thefe neceffary properties can
be acquired; with the afiiftance of this no difficulty will be
found.
Thefe microfcopes are fometimes fitted up with a toothed rack
and pinion, for the more ready adjuftment of the glaffes to their
proper focus.
P D escrip