SCIENTIFIC SUMMARY. 
259 
The increased colouring and distortion of the image, arising from the 
increased distance it had to traverse, have gradually been overcome by 
corresponding care in the construction of achromatic glasses ; and a series 
of improvements made during the last thirty years has culminated in an 
instrument, which for precision of adjustment and truth of definition has 
left scarce anything to be desired. 
The optical wonder, which merits this encomium, is known as “ Wenliam’s 
Binocular Microscope,” so called because, instead of peering with one eye 
down a single tube, as heretofore, the observer has the additional comfort, 
convenience, and advantage of looking with both eyes down a pair of tubes, 
so exquisitely adjusted, that the object is accurately and beautifully defined 
by the combination. This is, perhaps, the perfection of microscopy, and 
the scientific world is deeply indebted to the well-known and remarkable 
skill and ingenuity of Mr. F. H. Wenham for this marvellous instrument. 
Like all great discoveries, the binocular microscope was not the result of 
a lucky accident or guess, but of patient investigation and unwearied 
labour, and a perseverance undaunted by failure. 
The stereoscope, whose phenomena have so captivated the public mind, 
perhaps paved the way for the invention of a binocular microscope, for 
although the principles of the two instruments are dissimilar, the result 
arrived at was the same, viz. : to give to the object that aspect of solidity, 
which natural objects assume when viewed with our two eyes. The object 
of such a double arrangement of our visual organs being to enable us to 
see the same object under two aspects at the same time, these two aspects 
being separated by the distance between the two rays, but so combined in 
the brain as to produce a single image having an appearance of solidity. 
Now the difference between the stereoscope and the binocular microscope 
is simply this, that in the former we arrange two images in such a manner 
that we succeed in seeing them as they are not, whereas in the latter we 
succeed in arranging our two eyes, so that, looking at a single object, we see 
it as it really is — that is, relieved from the flatness which appears in objects 
viewed only with one eye. This, it will be seen at once, is an immense 
advantage, and Professor Riddell of New Orleans constructed an instru- 
ment which aimed at this result, but without practical success. Mr. Wen- 
ham then came into the field, but his first attempt, described in the second 
volume of “ Microscopic Journal,” N.S., was also far from attaining that per- 
fection of adjustment and definition which was essential to success. France 
also put in a claim, and M. Nachet produced a microscope free from many 
of the defects of Mr. Wenham’ s first attempt; and for low powers this 
wonderfully cheap instrument answers admirably, losing, however, its 
clearness of definition when high powers are used. 
The improved form of binocular, however, now introduced by Mr. 
Wenham, and which has entirely captivated all microscopical observers, 
does not essentially differ from his former instrument. The principal 
objection to that, was that the projecting portions of the object appeared 
sometimes to be depressed, and vice versd. The essential principle in all 
binoculars, is to bisect the pencils of rays which emerge from a single 
objective, each half being magnified and sent up in a separate tube to the 
two eyes, and each half of course differing in perspective projection ; the 
