286 
PROCEEDINGS OF THE SOCIETY. 
was suggested to me in private conversation, that as I had used but one 
maker’s lenses for my experiments it was not exhaustive enough, and 
that I might find the lenses of other makers give a different result. 
Feeling the force of this, and knowing the danger of generalizing from 
the particular, I applied to my friend Mr. E. M. Nelson to see if he 
could help me in this matter, and out of his splendid store of object- 
glasses lend me a selection of what might be called representative glasses. 
This he has kindly dono and by their help I have been able to push 
my experiments to what I trust is a definite conclusion. The glasses used 
are the folio wing : — 
1/4 in. Ross date 1836, N.A. *38, Initial Power 40 
1/4 
55 
Powell „ 
1841 
55 
•5 
55 
55 
48 
1/12 
55 
Ross „ 
abt. 1850 
55 
•81 
55 
55 
128 
1/6 
55 
Hartnack „ 
1872 
55 
•9 
55 
55 
67 
2/3 
55 
Powell „ 
1873-6 
55 
•28 
55 
55 
154 
1/12 
55 
Powell, W. F. „ 
1877 
55 
1-2 
55 
55 
135 
1/5 
55 
Gundlach „ 
1882-5 
55 
•88 
55 
55 
54 
The subjects chosen are the podura scale, P. angulaium , and the pro- 
boscis of blow-fly, according to the N.A. of the glasses used, but in all 
cases the results are in accordance with my former experiments. No 
screen or light-filter has been used, but the image always came out true 
to focus when an isochromatic plate was used, but more or less out of 
focus when a plate was used not colour-correct. I had but little hesita- 
tion before, but I have none now in asserting that the owner of any 
ordinary achromatic objective can produce, photographically, an image 
on the same plane as the visual rays, and that without any adjustment 
for focus or the use of any screen, provided always that he uses isochro- 
matic plates.” 
Prof. Bell read the following note on A Simple Illuminator for the 
Microscope, received from Dr. A. M. Edwards, of Newark, N.J., U.S. : 
— “ The plan of an illuminator for the Microscope was suggested by 
Dr. R. L. Maddox in the Journal of the Royal Microscopical Society, 
1890, p. 101. In it he uses a prism of glass ground down and placed 
beneath the object. I use what I believe to be cheaper, that is to say, a 
piece of glass rod such as is used by chemists for stirring solutions. 
A piece of glass rod, about 1/4 in. thick, is cut off about 1/2 in. long 
and ground, as it can be done on a stone hone, on the broken edges. 
It is also ground down along the flat to about 3/8 thick, that is to 
say, one-quarter is ground off, and as I use a fine hone a finely ground 
glass results. This is cemented by gum thus and oil of cinnamon, 
which is the common varnish of preservation I use now, to the under 
side of a common glass slide. But the slide is prepared first ; it has a 
coating of diamond dye of a dark blue colour put on first ; this must not 
be too dark but dark enough to tint the light bluish. This is used 
with oil of cinnamon between it and the slide with the object on. 
And the illumination is with a kerosene oil lamp ; perhaps an electric 
lamp is better, but that is expensive. I want to cheapen all the ap- 
paratus of the Microscope I can. This makes a good illuminator and, 
