PREFACE TO THE ORIGINAL EDITION. THE Author of this volume feels himself extremely happy in the opportunity which this publication affords him of acknowledging the obligations he is under to the authors of "Practical Education," for the pleasure and instruction which he has derived from that valuable work. To this he is indebted for the idea of writing on the subject of Natural Philosophy for the use of children. How far his plan corresponds with that suggested by Mr. Edgeworth, in his chapter on Mechanics, must be left with a candid public to decide. The Author conceives, at least, he shall be justified in asserting, that no introduction to natural and experimental philosophy has been attempted in a method so familiar and easy as that which he now offers to the public-none which appears to him so properly adapted to the capacities of young people of ten or eleven years of age; a period of life which, from the Author's own experience, he is confident is by no means too early to induce in children habits of scientific reasoning. In this opinion he is sanctioned by the authority of Mr. Edgeworth. "Parents," says he, "are anxious that children should be conversant with mechanics, and with what are called the mechanical powers. Certainly no species of knowledge is better suited to the taste and capacity of youth, and yet it seldom forms a part of early instruction, Every body talks of the lever, the wedge, and the pulley, but most people perceive, that the notions which they have of their a 2 respective uses are unsatisfactory and indistinct; and many endeavour, at a late period of life, to acquire a scientific and exact knowledge of the effects that are produced by implements which are in everybody's hands, or that are absolutely necessary in the daily occupations of mankind." The Author trusts that the whole work will be found a complete compendium of natural and experimental philosophy, not only adapted to the understandings of young people, but well calculated also to convey that kind of familiar instruction which is absolutely necessary, before a person can attend public lectures in these branches of science with advantage. "If," says Mr. Edgeworth, speaking on this subject, "the lecturer does not communicate much of that knowledge which he endeavours to explain, it is not to be attributed either to his want of skill or to the insufficiency of his apparatus, but to the novelty of the terms which he is obliged to use. Ignorance of the language in which any science is taught is an insuperable bar to its being suddenly acquired: besides a precise knowledge of the meaning of terms, we must have an instantaneous idea excited in our minds whenever they are repeated: and, as this can be acquired only by practice, it is impossible that philosophical lectures can be of much service to those who are not familiarly acquainted with the technical language in which they are delivered.” It is presumed that an attentive perusal of these Dialogues, in which the principal and most common terms of science are carefully explained, and illustrated by a variety of familiar examples, will be the means of obviating this objection with respect to persons who may be desirous of attending those public philosophical lectures to which the inhabitants of the metropolis have almost constant access V. Definitions-Different kinds of Lenses-Mr. Parker's Burning Lens, and the effects produced by it VIII. Nature and Advantages of Light Of the separation X. Reflected Light and Plane Mirrors XI. Concave Mirrors-Their Uses, and mode of Action 425 |