ast, which is supplied by the
_first_ microscopic makers. I cannot help thinking that this substitution
will prove of some service; for, in the first place, the power of the
condenser is generally equal to that of a quarter of an inch object-glass,
which is perhaps the most generally useful of all the powers; and again,
its aperture is, I think, not usually so great as that which an
object-glass of the same power would have; and, moreover, as to correction,
though it is slightly spherically under-corrected to accommodate the
plate-glass under the object, yet the chromatic correction is _perfect_.
The condenser is easily detached from its "fittings," and its application
to the camera would be as simple as that of an ordinary object-glass.

However, my conviction remains that, in spite of all that perseverance and
science can accomplish, it never will be in the power of the photographer
to produce a picture of an object under the microscope, _equally distinct
in all its parts_; and unless his art can effect this, I need scarcely say
that his best productions can be but useful auxiliaries to the draughtsman.

I see by an advertisement that the Messrs. Highley supply everything that
is necessary for the application of photography to the microscope.

H. C. K.

---- Rectory, Hereford.

In reply to your correspondent J., I would ask if he has any photographic
apparatus? if so, the answer to his question "What extra apparatus is
required to a first-rate microscope in order to obtain photographic
microscopic pictures?" would be _None_; but if not, he would require a
camera, or else a wooden conical body, with plate-holder, &c., besides the
ordinary photographic outfit. Part III. of the _Microscopical Journal_,
published by Highley & Son, Fleet Street, will give him all the information
he requires. {557}

[phi]. (p. 506.) may find a solution of his difficulties regarding the
production of stereoscopic pictures, in the following considerations. The
object of having two pictures is to present to _each eye_ an image of what
it sees in nature; but as the angle subtended by a line, of which the
pupils of the eyes form the extremities, must differ for every distance,
and for objects of varying sizes, it follows there is no _absolute_ rule
that can be laid down as the only correct one. For _distant_ views there is
in nature scarcely any stereoscopic effect; and in a photographic
stereoscopic view the effect produced is not really a