299 
’Pror. D. S. Martin exhibited some Silver Images from 
Nicaragua, which Mr. Squier recognized as of modern origin ; 
being very commonly used as votive offerings. 
The following paper was read, and the various apparatus 
mentioned in it, exhibited. 
Description of a new form of Achromatic Prism for illuminating 
Microscopic Objects. 
By Pror, A. M. Epwarps. 
It is my intention, at the present time to merely describe 
the form of apparatus I have contrived for the purpose of 
illuminating microscopic objects so as to bring out certain 
details not otherwise readily made evident, whilst I leave for 
some future time the consideration of the results arrived at in 
special cases. For the information of those microscopical 
observers who are interested in examining the so-called “ Test 
objects,” and also as of interest to students of the Diatomacee, 
I must mention that a year or more before Mr. Hartnack pub- 
lished his paper on the structure of the shell of Surrirella gemma, 
wherein he states (and gives figures to prove his assertion) that 
he resolved the markings on that ‘hitherto considered difficult 
test, into “‘ elongated hexagons,” I had satisfactorily made out 
for myself, and shown to others, who agreed with me, that the 
markings consisted of equilateral hexagons, after the manner 
of those seen on TJricertiwm favus, but which could be made 
to appear “elongated” by a change of focus or mode of 
illumination. This result was achieved by using a contri- 
vance similar to that Iam about to describe in this paper. 
To make this paper fully understood it would be desirable 
to enter somewhat into the consideration of the illumination 
of transparent, finely-sculptured objects generally on the 
stage of the microscope, but it is too vast a subject 
to be treated of properly within the scope of a communica- 
tion like the present. I must, therefore, confine myself to 
saying something historical in the form of an introduction, 
