ace between particles
which are _similar_, and the latter between those which are
_dissimilar_. All the operations of chemistry are founded upon the
force of affinity which Nature has established between the particles
of different kinds of matter, and which enables the chemist to produce
_new_ compounds differing more or less from the substances by whose
union they were formed.

Is it, then, necessary for chemists to understand the relative nature
of all substances?

Yes; because the basis of this science consists in an _analytical_
examination of the works of Nature; an investigation of the properties
and uses of all substances we are acquainted with; and the study of
the effects of _heat_ and _mixture_, in order that we may find out
their general and subordinate laws.

_Analytical_, relating to analysis.

_Investigation_, act of searching, or tracing out.

_Subordinate_, inferior in nature, dignity or power.

Relate a few more of the advantages obtained by a knowledge of
Chemistry.

Many of the wonderful operations of Nature, and the changes which take
place in substances around us, are, by its means, revealed to us. In
every manufacture, art, or walk of life, the chemist possesses an
advantage over his unskilled neighbor. It is necessary to the farmer
and gardener, as it explains the growth of plants, the use of manures,
and their proper application: and indispensable to the physician, that
he may understand the animal economy, and the _effects_ which certain
_causes_ chemically produce; and the nature of animal, vegetable, and
mineral poisons. The study is, therefore, an invaluable branch in the
education of youth: it is useful, not only in the active, but the
_moral_ life, by laying the foundation of an ardent and inquiring
mind. Even an everyday walk in the fields can be productive of
instruction, by a knowledge of it;--and let us always remember, that
"Knowledge is Power."

_Indispensable_, necessary, not to be done without.

CHAPTER XIX.

ATTRACTION, TIDES, GRAVITY, ARTESIAN WELLS, AIR, ANEROID
BAROMETER, EAR-TRUMPET, STETHOSCOPE, AUDIPHONE, TELEPHONE, PHONOGRAPH,
MICROPHONE, MEGAPHONE, TASIMETER, BATHOMETER, ANEMOMETER,
CHRONOMETER.

What is Attraction?

By attraction is meant that property or quality in the particles of
bodies which makes them tend toward each other.

Are there several kinds of attraction?

Yes. Attraction has received different names, acco