Gu, 1798") 
I—The Exhibitor: a Novel Apparatus for showing Diatoms, &e. 
By the Hon. and Rey. the Lord 8. G. Osnornz, B.A., F.R.M.S. 
Witx you kindly permit me to introduce to your readers a little 
addition to the apparatus of a microscope, which I am sure will 
well repay its cost, and the little practice in its manipulation, 
required for its perfect success. 
In nearly thirty years’ enjoyment of the microscope—using it 
for many hours on the greater proportion of my days, applying it 
to all kinds of investigation—I always coveted some simple means 
of getting a good oblique light for illuminating, under the higher 
powers. I have bought and borrowed a good many ingenious in- 
ventions for the purpose, and have generally succeeded in getting 
fair results, but always with more trouble than was quite agree- 
able, to say nothing of the expensive nature of the means used. 
After a great deal of experiment, and much hard work, with very 
indifferent tools, I am at last quite satisfied. I have for the last 
few months had more enjoyment from the microscope than I ever 
had before, and this from a very simple contrivance. The Dia- 
tomacez I had observed under other modern inventions, but until 
now I never saw their real beauty, or got such satisfactory informa- 
tion as to their construction. 
I will now give the plainest description I can of “ the Exhibitor.” 
I take a “Darker” stage, as used for polarizing. I have two 
counter-sinkings made on its stage front in the revolving ring; 
one, the top one, rather larger in circumference and shallower than 
the lower one. Into the lower “sinking” I drop a disk of 
blackened metal with a small kettledrum lens mounted in the 
centre. Into the upper “sinking” I place metal disks with certain 
apertures made in them; the front of these disks is just level with 
the face of the stage, the back close to the front of the disk holding 
the small lens. 
I have a fine screw-worm cut into the back part of the re- 
volving ring, coming up just below the lower counter-sinking. Into 
this screws a ring of brass carrying a bull’s-eye or kettledrum lens, 
of about the diameter of a shilling. The screw movement having 
a milled edge, it can thus be focussed as required with the small 
upper one. 
It will be at once seen that the Exhibitor is thus nothing more 
complex than a Darker stage with two kettledrums, the larger 
receiving the light from the lamp, transmitting it to the small 
one, which latter then delivers it at the back of the metal disk 
which is flush with the front of the stage, the screw movement 
enabling the observer to focus the two drums. 
As to the apertures to be cut in the metal disks, after a great 
