CONVERSATIONS ON NATURAL PHILOSOPHY

PREFACE.


Notwithstanding the great number of books which are written, expressly
for the use of schools, and which embrace every subject on which
instruction is given, it is a lamentable fact, that the catalogue of
those which are well adapted to the intended purpose, is a very short
one. Almost all of them have been written, either by those who are
without experience as teachers, or by teachers, deficient in a competent
knowledge of the subjects, on which they treat. Every intelligent
person, who has devoted himself to the instruction of youth, must have
felt and deplored, the truth of these observations.

In most instances, the improvement of a work already in use, will be
more acceptable, than one of equal merit would be, which is entirely
new; the introduction of a book into schools, being always attended with
some difficulty.

The "Conversations on Chemistry," written by Mrs. Marcet, had obtained a
well-merited celebrity, and was very extensively adopted as a
school-book, before the publication of her "Conversations on Natural
Philosophy." This, also, has been much used for the same purpose; but,
the observation has been very general, among intelligent teachers, that,
in its execution, it is very inferior to the former work.

The editor of the edition now presented to the public, had undertaken to
add to the work, questions, for the examination of learners; and notes,
where he deemed them necessary. He soon found, however, that the latter
undertaking would be a very unpleasant one, as he must have pointed out
at the bottom of many of the pages, the defects and mistakes in the
text; whilst numerous modes of illustration, or forms of expression,
which his experience as a teacher, had convinced him would not be clear
to the learner, must, of necessity, have remained unaltered. He
therefore determined to revise the whole work, and with the most perfect
freedom, to make such alterations in the body of it, as should, in his
opinion, best adapt it to the purpose for which it was designed. Were
the book, as it now stands, carefully compared with the original, it
would be found, that, in conformity with this determination, scarcely a
page of the latter, remains unchanged. Verbal alterations have been
made, errors, in points of fact, have been corrected; and new modes of
illustration have been introduced, whenever it was thought that those
already employed, could be improved; or when it was known, that, from
local causes, they are not familiar, in this country.

The editor feels assured, that, in performing this task, he has rendered
the book more valuable to the teacher, and more useful to the pupil; and
he doubts not that the intelligent author of it, would prefer the mode
which has been adopted, to that which was at first proposed.

The judicious teacher will, of course, vary the questions according to
circumstances; and those who may not employ them at all, as questions,
will still find them useful, in directing the pupil to the most
important points, in every page.

The Glossary has been confined to such terms of science as occur in the
work; and is believed to include all those, of which a clear definition
cannot be found in our common dictionaries.




CONTENTS.


CONVERSATION I.

ON GENERAL PROPERTIES OF BODIES. 9

INTRODUCTION. General Properties of Bodies. Impenetrability.
Extension. Figure. Divisibility. Inertia. Attraction.
Attraction of Cohesion. Density. Rarity. Heat. Attraction of
Gravitation.


CONVERSATION II.

ON THE ATTRACTION OF GRAVITY. 22

Attraction of Gravitation, continued. Of Weight. Of the Fall of
Bodies. Of the Resistance of the Air. Of the Ascent of Light
Bodies.


CONVERSATION III.

ON THE LAWS OF MOTION. 32

Of Motion. Of the Inertia of Bodies. Of Force to produce
Motion. Direction of Motion. Velocity, absolute and relative.
Uniform Motion. Retarded Motion. Accelerated Motion. Velocity
of Falling Bodies. Momentum. Action and Reaction equal.
Elasticity of Bodies. Porosity of Bodies. Reflected Motion.
Angles of Incidence and Reflection.


CONVERSATION IV.

ON COMPOUND MOTION. 46

Compound Motion, the result of two opposite forces. Of
Curvilinear Motion, the result of two forces. Centre of Motion,
the point at rest, while the other parts of the body move round
it. Centre of Magnitude, the middle of a body.