52 MEMORANDA. 
ture will be thrown further from the eye, and be very largely 
increased in size. The picture no longer seems to touch the 
end of the tube, but is formed far away from it. The effect 
altogether is to me astonishing. 
I proceed in this way :—I use the second pair of eye-pieces 
with the l-inch objective. I draw them as far out of the 
tube as they will bear, to: hold, and, as they fit rather loosely, 
I grasp the two eye-pieces with my left hand, and bring them 
as parallel as I can, when the picture will instantly start off 
to a great distance and become magnified; and if the left- 
hand eye-piece is moved backwards and forwards, 7. e. from 
left to right, &c., the image will alternately approach and 
diminish, and recede aud enlarge, in a strange way. 
This is a subject which requires both physiological and 
mathematical investigation. For the absolute truth of the 
principle I can vouch.—Reyv. J. Maynarp, Cape of Good 
Hope. 
Ar a soirée given by the Professors of University College 
on the 14th instant we had an opportunity of seeing the ap- 
plication of a new mode of illumination of opaque objects, 
when viewed by high powers, in an instrument exhibited by 
Messrs. Smith and Beck, and in one shown by Messrs. Powell 
and Lealand. The illumination was, we believe, effected in 
the same way in either case, although in Messrs. Smith and 
Beck’s instrument the object-glass was 1th, and in Messrs. 
Powell and Lealand’s ~,th. The effect was marvellously 
beautiful, and the definition of the object (the scales of some 
Coleopteron) remarkably good and distinct. The way in 
which this successful result was brought about is remarkably 
simple, consisting simply of a piece of thin plate glass intro- 
duced into the lower part of the tube, immediately above the 
object-glass, and placed in an oblique position, so that rays 
of light impinging upon its under surface, and received 
through a small lateral opening, and thrown down through 
the object-glass, and of course concentrated in the focus of 
the latter upon the object, whilst the transmission of the 
magnified image is not appreciably interfered with by their 
passage through the thin glass reflecting diaphragm. In the 
American contrivance for the same purpose the light is 
thrown down in the same way by a metallic reflector, which 
covers about one half of the object-glass, and thus, of course, 
destroys at least half of the illumination. The contrivance 
above described, we believe, was hit upon about the same time 
by the two celebrated firms we have named. 
