actinic ray, which shine in modes differing
from each other and from the rest of their
sun-born brethren; it is even said that the
photographic ray is more powerful in the
New World than in the Old. Amongst the
modern dissection of light may be named
what is called the polarised ray, and which
has been especially pressed into the ranks of
the microscope's auxiliaries. Man, the
all-appropriating animal, has thus cunningly
forwarded his ends by catching at what
might be called the impurities of the
"quintessence pure."

The modern improvements of the microscope
(one of the most important of which
is the construction of achromatic object-glasses,
first successfully attempted by Monsieur
Selligues, of Paris, in eighteen hundred
and twenty-three) have rendered the difference
between old and modern treatises on
the microscope, and old and modern accessory
apparatus, immense. Even the best of
compound microscopes, a hundred years ago,
were simple and obvious in their construction
and uses. Even with the overflowing
luxury of half-a-dozen different object-glasses,
as in Cuff's chef-d'Å“uvre described by Baker,
there was no combination of their power, no
union of their effect; they could merely be
used in succession, on separate occasions,
according as each respective object investigated
required to be more or less magnified.
They had a glass for a flea, and a glass for a
wheel animalcule; but they dared not
attempt the feat which Nature is said to have
executed when she required an improved
specimen of epic poet,—to make a third, they
ventured not to join the other two; for the
result would have been coloured fringes and
confusion. While, of many modern optical
luxuries, our forefathers no more dreamt than
they did of collodion photography, or
Atlantic electric cables. Indeed, so varied and
numerous are now the aids to the
microscopist, that their very purpose and mode of
application is a difficult puzzle to observers,
who have looked, and been edified by looking,
through simples and compounds of
eighteenth-century construction. You may
even put the possessor of a modern microscope
of only moderate pretensions before a
first-class instrument, costing from thirty to
a hundred guineas with its fitting, in its
sleek Spanish mahogany case; and, on bringing
his hidden treasure to light, he will find
the utmost difficulty in directing its
movements, so as to see anything with it. He
will open its richly stored drawer or
drawers, and be dazzled by the glittering
trinkets within, and will have as little idea
as to how they are to be worn by the regal
microscope (that is, where they are to be
screwed on, inserted, and placed), as an
Addiscombe cadet would have, on inspecting
the jewel-box of an Indian begum, or a
Mantchoo princess whom he were suddenly
called upon to deck appropriately with her
native collection of silks, gems and other
finery.

Students are now guided in their manipulations
of the microscope by various treatises,
amongst which, Dr. Carpenter's wonderful
book, and Beale's lectures are specially excellent;
the catalogues of the principal makers
are also well worth careful perusal and
reference; but there is one set of shining
microscopic baubles on which I should like
to say a few words, both on account of their
being somewhat charily mentioned by the
writers referred to, and mainly because they
constitute a talisman whose influence is
magical, if natural magic be still allowed to
exist.

In a former article in this volume, it was
stated* that if the reader wished to test
the attractiveness as well as the portability
of modern microscopes, he should arrive some
rainy day at a country house full of company,
when the guests were prevented from enjoying
out-door amusements, with one of
Amadio's forty guinea instruments, accompanied
by a boxful of good preparations,—
on producing which, he would work wonders.
One of the means of displaying his marvels
would be the apparatus for the polarisation
of light. The price and the maker are thus
specially named in order to speak of what I
know,—as also to indicate that the polariscope
is only affixed to instruments of a
superior order, and not to students'
microscopes of moderate price, which latter may
yet be eminently useful for working with
ordinary light. Amadio's lowest priced
instrument, capable of carrying a polariser, is
seven pounds ten shillings, Smith and Beck's
educational microscope admits the addition
of a polarising apparatus complete, at the
additional charge of a guinea and a-half. Of
the efficiency of this there can be no doubt,
any more than of those supplied by the
other great makers, as Mr. Ross, or Messrs.
Powell and Lealand.  The instrument
employed for polarisation mostly consists of
three articles; videlicet, a prism of
Iceland spar, called the polariser, fixed in a
revolving cylinder, to go below the object;
a selenite object-carrier, to be laid on the
stage, and on which the object to be examined
is laid; and thirdly, the body-prism, or
analyser, also of Iceland spar, which is
inserted at the bottom into the body of the
microscope, and, consequently, above the
object. Suppose, then, that your microscope
stands before you, and that you are wishing
to observe with polarised light; remove the
diaphragm plate, and take, with the intention
of putting it in its place, the one that
has the rack adjustment, or cylinder-fitting
(used also with the achromatic condenser,
and the spotted lens). Into this plate, screw
the polariser, and then insert them beneath
the stage; unscrew the adapter at the bot-

* Page 138.