ing it in
small amounts, our rainfall would seem to offer an ample supply. These
facts open our eyes to the possible fertilizing influence of rains, and
they also suggest to what extent rains may exert a corrosive action when
they descend charged with acid vapors.--_L.P. Gratacap, in School of
Mines Quarterly_.

* * * * *

THE CHROMATOSCOPE.

Some time ago Mr. J.D. Hardy devised an instrument, which he has named a
chromatoscope, so easily made by any one who has a spot lens that we
take the following description from the _Journal_ of the Royal
Microscopical Society: "Its chief purpose is that of illuminating and
defining objects which are nonpolarizable, in a similar manner to that
in which the polariscope defines polarizable objects. It can also be
applied to many polarizable objects. This quality, combined with the
transmission of a greater amount of light than is obtainable by the
polariscope, renders objects thus seen much more effective. It is
constructed as follows: Into the tube of the spot lens a short tube is
made to move freely and easily. This inner tube has a double flange, the
outer one, which is milled, for rotating, and the inner one for carrying
a glass plate. This plate is made of flat, clear glass, and upon it are
cemented by a very small quantity of balsam three pieces of colored
(stained) glass, blue, red, and green, in the proportion of about 8, 5,
and 3. The light from the lamp is allowed to pass to some extent through
the interspaces, and is by comparison a strong yellow, thus giving four
principal colors. Secondary colors are formed by a combination of the
rays in passing through the spot lens.

"The stained glass should be as rich in color and as good in quality as
possible, and a better effect is obtained by three pieces of stained
glass than by a number of small pieces. The application of the
chromatoscope is almost unlimited, as it can be used with all objectives
up to the 1/8. Transparent objects, particularly crystals which will not
polarize, diatoms, infusoria, palates of mollusks, etc., can not only be
seen to greater advantage, but their parts can be more easily studied.
As its cost is merely nominal, it can be applied to every instrument,
large or small; and when its merits and its utility by practice are
known, I am confident that it will be considered a valuable accessory to
the microscope."

* * * * *

Prof