CHAPTER XVII.

ON MECHANICS.

PARENTS are anxious that children should be conversant with Mechanics, and with what are called the mechanic 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 when they wish to employ these organs, they frequently perceive that the notions which they have of their 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 every body's hands, or that are absolutely necessary in the daily occupations of mankind.

An itinerant lecturer seldom fails of having a numerous and attentive auditory, and if he 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 ac quired; 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; and yet there is scarcely any subject of human inquiry more obvious to the understanding than the laws of mechanics. Only a small portion of

geometry is necessary to the learner, if he even wishes to become master of the more difficult problems which are usually contained in a course of lectures; and most of what is practically useful may be acquired

by any person who is expert in common arithmetic.

But we cannot proceed a single step without deviating from common language; if the theory of the balance, or the lever, is to be explained, we immediately speak of space and time. To persons not versed in literature it is probable, that these terms appear more simple and intelligible than they do to a man who has read Locke, and other metaphysical writers. The term space, to the bulk of mankind, conveys the idea of an interval; they consider the word time as representing a definite number of years, days, or minutes; but the metaphysician, when he hears the words space and time, immediately takes the alarm, and recurs to the abstract notions which are associated with these terms; he perceives difficulties unknown to the unlearned, and feels a confusion of ideas which distracts his attention. The lecturer proceeds with confidence, never supposing that his audience can be puzzled by such common words. He means by space the distance from the place whence a body begins to move to the place where its motion ceases; and by time

he means the number of seconds, or of any determinate divisions of civil time which elapse from the commencement of any motion to its end; or, in other words, the duration of any given motion. After this has been frequently repeated, any intelligent person perceives the sense in which these terms are used by the tenor of the discourse; but in the interim the greatest part of what he has heard cannot have been understood, and the premises upon which every subsequent demonstration is founded are unknown to him. If this be true when it is affirmed of two terms only, what must be the situation of those to whom eight or ten unknown technical expressions occur at the commencement of a lecture? A complete knowledge, such a knowledge as is not only full, but familiar, of all the common terms made use of in theoretic and practical mechanics, is, therefore, absolutely necessary before any person can attend-public lectures in natural philosophy with advantage.

What has been said of public lectures may, with equal propriety, be applied to private instruction; and, it is probable, that

inattention to this circumstance is the reason why so few people have distinct notions of natural philosophy. Learning by rote, or even reading repeatedly, definitions of the technical terms of any science, must undoubtedly facilitate its acquirement; but 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 acquirement of science.

The ancients, in learning this species of knowledge, had an advantage of which we are deprived many of their terms of science were the cominon names of familiar objects. How few do we meet who have a distinct notion of the words radius, angle, or valve? A Roman peasant knew what a radius or a valve meant, in their original signification, as well as a modern professor; he knew that a valve was a door, and a radius a spoke of a wheel; but an English child finds it as difficult to remember the meaning of the word angle, as the word parabola. An angle is usually confounded, by those who are ignorant of geometry and mechanics, with the