eter of a driven pulley that shall make any given number
of revolutions in the same time: Multiply the diameter of the driving
pulley by its number of revolutions, and divide the product by the
number of revolutions of the driven pulley.

A piece of the well-known tar soap held against the inside of a belt
while running will prevent it from slipping, and will not injure the
belt.

Boiler scale is composed of the carbonate or the sulphate of lime. To
prevent the formation it is necessary to use some substance which will
precipitate these elements in the water. The cheapest and most
universally used for this purpose are soda ash and caustic soda.

Gold bronze is merely a mixture of equal parts of oxide of tin and
sulphur. To unite them they are heated for some time in an earthen
retort.

Rusted utensils may be cleaned of rust by applying either turpentine or
kerosene oil, and allowing them to stand over night, when the excess may
be wiped off. Clean afterwards with fine emery cloth.

Plaster of paris is valuable for many purposes in a machine shop, but
the disadvantage in handling it is, that it sets so quickly, and its use
is, therefore, very much limited. To prevent quick setting mix a small
amount of arrow root powder with the plaster before it is mixed, and
this will keep it soft for some time, and also increase its hardness
when it sets.

For measuring purposes a tablespoon holds 1/2 ounce; a dessertspoon 1/4
ounce; a teaspoon 1/8 ounce; a teacupful of sugar weighs 1/2 pound; two
teacupsful of butter weigh 1 pound; 1-1/3 pints of powdered sugar weigh
1 pound; one pint of distilled water weighs 1 pound.

Ordinarily, 450 drops of liquid are equal to 1 ounce; this varies with
different liquids, some being thicker in consistency than others, but
for those of the consistency of water the measure given is fairly
accurate.

CHAPTER XIV

THE SIMPLICITY OF GREAT INVENTIONS, AND OF NATURE'S MANIFESTATIONS

If there is anything in the realm of mechanics which excites the wonder
and admiration of man, it is the knowledge that the greatest inventions
are the simplest, and that the inventor must take advantage of one law
in nature which is universal in its application, and that is vibration.

There is a key to every secret in nature's great storehouse. It is not a
complicated one, containing a multiplicity of wards and peculiar angles
and recesses. It is the very simplicity in most of the problems which
long