INTENDED FOR THE

INSTRUCTION AND ENTERTAINMENT

OF

YOUNG PEOPLE:

IN WHICH

THE FIRST PRINCIPLES

OF

Datural and Experimental Philosophy

ARE FULLY EXPLAINED.

VOL. III. OF OPTICS, MAGNETISM,
ELECTRICITY, & GALVANISM.

"Conversation, with the habit of explaining the meaning of words ❝ and the structure of common domestic implements to children, is "the sure and effectual method of preparing the mind for the ac*6 'quirement of science." Edgeworth's Practical Education.

BY THE REV. J. JOYCE.

NEW EDITION CORRECTED AND IMPROVED.

PHILADELPHIA:

PUBLISIJED BY M. CAREY, ISAAC PEIRCE, JOHNSON & WARNER, KIMBER & RICHARDSON, B. C. BUSBY, EMMOR KIMBER, BENNET & WALTON, EDWARD PARKER.

THE NEW YORK!
PUBLIC LIBRARY

ASTOR, LENOX AND TILDEN FOUNDATIONS. 1909

A. Griggs & K. Dickinson, Printers. Whitehall.

ΤΟ

ANNA LETITIA BARBAULD

AND

JOHN AIKIN, M. D.

AUTHORS

OF

"EVENINGS AT HOME,"

AND

OTHER ADMIRABLE WORKS

FOR

THE INSTRUCTION OF YOUNG PERSONS.

THE

THIRD VOLUME

OF

SCIENTIFIC DIALOGUES.

ARE

RESPECTFULLY INSCRIBED,

BY

THE AUTHOR.