WiLLiAMSj on the Martin Microscope. 39 
is extremely ingenious^ and might possibly give a useful hint 
to microscope-makers now at the present time. 
But the body of the instrument can also be inclined^ so as 
to be at right angles with the triangular bar_, and, when in this 
position, another piece of apparatus can be applied to it, con- 
sisting of a frame carrying a bar for supporting a stage or 
pair of forceps, adjustable by means of a rack and pinion. 
Two stages of different sizes, and a pair of forceps, fit into it. 
It has also two motions besides that given by the rack and 
pinion just mentioned, one upon itself, in a horizontal direc- 
tion, the other perpendicular to this, by means of a small rack 
and pinion at the side. This arrangement is evidently intended 
for viewing objects by direct light. A reflecting mirror can 
also be applied to it, and it is possible to produce very oblique 
illumination by means of the motions I have described. 
Another piece of apparatus remains to be noticed. It con- 
sists of a tube, at the bottom of which is a concave speculum. 
There is an opening at the side of this tube, and also the 
means of applying a pair of hand forceps which can be brought 
into the focus of the speculum by means of a rack and pinion. 
Upon taking away that portion of the body which carries the 
powers, and screwing this on in its place, we have the instru- 
ment described by Martin in his optical works as the catadi- 
optric microscope. In this instrument, the object being 
strongly illuminated tlirough the opening at the side, the 
image is reflected by the speculum to the upper part of the 
tube, where it is viewed by means of the eye-piece. I found 
it very difficult to manage, and, although the image of the 
object was clear and tolerably distinct, its performance was 
not to me satisfactory ; but this may have been occasioned 
by want of experience in the proper mode of managing the 
instrument. 
There are several other pieces of apparatus in the drawers 
and boxes, the use of which does not appear, and some of 
these I believe not to belong to the instrument, as they 
cannot be applied to any part of it, as far as I can at present 
judge. 
I have thus endeavoured to give you some idea of the con- 
struction and appliances of this instrument, and, in conclusion, 
I may be expected to say something respecting its capabilities 
as a microscope. In doing this, I must premise that it 
would hardly be fair to attempt a comparision between it — 
although, undoubtedly, one of thebest instruments of its time — 
and the present, in every respect, vastly superior microscopes. 
We must therefore keep in mind, not only the immense 
stride that has been made within the last thirty years, in the 
