Dr. North on the Binocular Microscope. 63 
adapted to different planes; while in the common stereoscope the 
impression of a solid object is, as we have before said, absolutely 
perfect ; so that when an object is deeper than it is long or broad 
it will infallibly appear so, and we are enabled even to measure 
the depth, to a certain extent, by comparing it with the length or 
breadth as a unit. 
Professor Riddell has practically succeeded in adding to the 
previous powers of the microscope all e of the other instru- 
ment now so common and popular; and with this great superi- 
ority, that whereas the latter can exhibit only pictures and those 
of large objects, being thus dependent on the accuracy of the 
drawing, or the success of the photograph, his binocular micro- 
scope exhibits minute objects themselves with perfect accuracy 
and truth as they exist in nature; presenting them as solids in 
which the dimension of depth or thickness and their distance in 
superposition, is of as much importance to truth of perception as 
Mr. Grunow an instrument of great beauty of workmanship and 
convenience, the performance of which is most satisfactory in - 
reference to the objects aimed at. 
For a full description of the optical arrangement by which 
binocular vision is attained, we refer the reader to Prof. Riddell’s 
article on the “ Binocular Microscope,” read before the American 
Association for the Advancement of Science, July, 1853, and pub- 
lished in No, 5, of the Quarterly Journal of Microscopical Science. 
_ As far as we have been able to observe, this arrangement is not 
liable, in any degree, to the charge of pseudoscopy, nor is any 
perceptible chromatic or spheroidal aberration produced by the 
interposition of prisms, which is sufficiently proved by the exam- 
ination of minute mercury-globules. 
Perlormed by rack and pinion, and are so arranged that they act 
equally and at the same time on both the right and left side. 
he image is inverted in one direction, and two small rect. prisms 
ed above the eye-pieces, make it appear in its natural position 
and thus adapt the instrument for dissecting. 
