34 
WiLLiAMS_, on the Martin Microscope. 
pound ones. In this opinion tlie editor is disposed to concur/' 
This passage is curious^ inasmuch as it not only shows that 
Martin had attempted to produce achromatic object-glasses 
for microscopes^ in which he appears to have failed_, but 
also gives the opinion of the editor^ who was well known as 
a microscopical observer,, in 1828^ as to the inferiority of 
achromatic combinations when compared with single lenses, 
an opinion which subsequent experience has most trium- 
phantly refuted. 
Such is the information I have been able to collect re- 
specting the maker of this, for the time, magnificent instru- 
ment, and I will now proceed to give you the result of my 
examination of it. In doing this, I have first to call your 
attention to the stand. This consists principally of a stout 
bar, the greater portion of which is triangular, each side 
being 1^ inch. This supports the body carrying the eye- 
piece, the stage, mirror, &c. The lower extremity of this bar 
is let into a tripod-stand, on which it turns. Just above the 
top of this tripod-stand, there is a strong hinge-joint in the 
bar, which is moved by means of a rack and pinion, and thus 
the observer is enabled to incline the instrument to a conve- 
nient angle. At the back of the triangular portion of the 
bar is a strong rack in which two pinions work. These raise 
or depress the stage and mirror, as may be required. At the 
top of the bar is a moveable cap, which carries an arm for the 
support of the body containing the eye-piece. This arm has 
a movement perpendicular to the bar, effected by means of a 
rack and pinion, and lateral motion is also given to it by 
similar means applied to the side of the head, and thus every 
part of an object can be subjected to inspection without dif- 
ficulty, and the necessity of a moveable stage obviated. 
The stage is simply a perforated plate, having ornamental 
scroll-work round it, in which are holes for forceps, condenser, 
&c., and also a clip beneath it for holding the frog-plate and 
other apparatus, which will be shortly described. On it the 
following inscription is engraved : — "B. Martin, Invt. et Fecit, 
London,'^ but there is no date. This, from the workmanship, 
I should fix at about 1770. A spring stage of the usual con- 
struction of that period, for holding the slides containing 
objects, can be fitted into the central aperture, and there are 
also a spring stage with a condenser, disks of glass and 
ivory, and other apparatus which fit into the same. The 
mirror is large and is double, being concave on the one side 
and plane on the other. It has beneath it a clip, probably 
for a condenser, as I can see no other use for it ; but as 
no condenser can be found among the apparatus at present 
