58 Description of an improved Microscope. [Jan.. 
level with the great mirror, and about two feet distant from it, so 
that the light may meet the long axis of the ellipse at a right 
angle ; then every thing goes on as before; and I think the 
transparent part of the instrument especially is never seen to 
more advantage than in this way. The vision altogether is very 
superior to that of the common lucernal, which is always full of 
colour, very indistinct, and distorted at the edges of the field. 
Our instrument will not, however, produce any image in the 
camera by lamp light—at least, it is a mere shadow, I have 
tried every possible kind of microscope, simple and compound, 
to endeavour to get'a decent image by lamp light, but have been 
totally unsuccessful ; the reason of which seems to be this: If 
you allow the apertures of the lenses sufficient diameter to give 
a requisite quantity of light, the image is quite confused, and 
full of colour; if you reduce them to the proper standard, the 
lamp will not afford light to show it, and here the matter rests. 
Incidit in Scyllam, &c. The utmost which can be done is to 
produce an image of a transparent object (an opaque one is out 
of the question), of which you are enabled to see the outline and 
something of the colour very slightly magnified ; but into the 
texture and minutie of which, you can see nothing. Of this 
description is the image of a common lucernal; and, in my 
opinion, it is not worth looking at. The only remedy for this 
which occurs to me, would be a lamp which should give as much 
light close to the instrument as the sun does at his natural distance. 
The best way to procure an image by lamp light in our micro- 
scope is to take the opaque body at its lowest power to view a 
transparent object (as this body gives much more light than the 
other), then to get a high stoo! and place it upon the table with 
the lamp opposite the large mirror, and proceed as with the sun. 
The camera must be quite dark. An image will be formed so 
that any body may affirm the instrument produces an image by 
candle light ; but this is all that can be said of it. 
It would not be amiss in packing the microscope to keep the 
opaque apparatus distinct from the transparent, so that a person 
imexperienced in microscopes might more readily learn to manage 
it: from the variety of purposes to which it is subservient, it is 
somewhat more complicated in its construction than microscopes 
usually are. 
I have neglected to describe a kind of slider which I use in 
my microscope ; it is composed of a glass tube, flattened, and 
drawn out to the size of a common slider, and polished on one 
side: its use is to hold microscopical objects which will not 
keep in a dry state, such as pieces of finely injected membrane, 
petals of flowers, and the like; these little preparations are intro- 
duced into the slider, which is then filled with spirits, and 
covered at the end with a bit of bladder secured by a wax 
thread. / 
I now proceed to fig. 3, which isa compound rhicroscope, which 
