y nerves.

TASTE.--So with the sense of taste. The tongue is covered with minute
cells surrounded by nervous filaments which are set in motion whenever
any substance is brought into contact with the surface. Tasting is
merely the movement of these filaments, of greater or less rapidity.

If an article is tasteless, it means that these filaments do not
vibrate. These vibrations are of two kinds. They may move faster or
slower, or they may move in a peculiar way. A sharp acute taste means
that the vibrations are very rapid; a mild taste, slow vibrations.

When a pleasant taste is detected, it is only because the filaments are
set into an agreeable motion. The vibrations in the tongue may become so
rapid that it will be painful, just as a shriek becomes piercing to the
ear, or an intense light dazzling to the eye; all proceed from the same
physical force acting on the brain.

COLOR.--Color, that seemingly unexplainable force, becomes a simple
thing when the principles of vibration are applied, and this has been
fully explained by the spectroscope and its operation.

When the boy once appreciates that this force, or this motion in nature
is just as simple as the great inventions which have grown out of this
manifestation, he will understand that a knowledge of these things will
enable him to utilize the energy in a proper way.

CHAPTER XV

WORKSHOP RECIPES AND FORMULAS

In a work of this kind, dealing with the various elements, the boy
should have at hand recipes or formulas for everything which comes
within the province of his experiments. The following are most carefully
selected, the objects being to present those which are the more easily
compounded.

ADHESIVES FOR VARIOUS USES.--Waterproof glue. Use a good quality of
glue, and dissolve it in warm water, then add one pound of linseed oil
to eight pounds of the glue. Add three ounces of nitric acid.

Leather or Card-board Glue. After dissolving good glue in water, to
which a little turpentine has been added, mix it with a thick paste of
starch, the proportion of starch to glue being about two to every part
of glue used. The mixture is used cold.

A fine Belt Glue. Dissolve 50 ounces of gelatine in water, and heat
after pouring off the excess water. Then stir in five ounces of
glycerine, ten ounces of turpentine, and five ounces of linseed oil
varnish. If too thick add water to suit.

For cementing Iron to Marble. Use 30 parts of Plaster of Paris, 10