INTRODUCTION TO PHYSICS. 



[PROPERTIES OF MATTER. 



and others, however ingenious they may be, have a great tendency, if followed to thoir logical consequences, lo 

 restore tho days of philosophical darkness, in which imagination was the iynis fiituits which led men astray from the 

 true path of induction. 



The leading properties of matter are Extension, Impenetrability, and Inertia, and they are characteristic ; for if but 

 one atom existed in the universe, it must necessarily have those. If more than one particle exist, two forces would 

 be called into operation. By that of gravitation, each particle would be attracted mutually ; by cohesion, the two 

 would unite, and so form a mass. Thus, by the attraction of gravitation, masses affect each other's position ; whilst 

 by the attraction of cohesion, the masses are themselves formed and held together. 



It will be most convenient to deal with these properties and forces individually ; and to this end it will be first 

 necessary to define the term "atom." 



ATOMS. The original signification of the term is simply, " that which cannot be divided. " To such an idea it has 

 been objected, that it is impossible to conceive any particle so small that it cannot be bi-sected or otherwise cut into 

 parts. Mathematical reasoning and demonstration have been adduced in support of this view ; and perhaps the most 

 ingenious attempt is that wherein the mutual relationship of parallel lines and angles are employed. As, however, 

 geometricians are compelled to assume that a point occupies no space that a line lias length, but no breadth so it 

 may be permitted to the physicist to assume, that an atom is such a particle of matter as to be indivisible by physical 

 means ; and in this sense the term " atom" will be in future employed by us. 



Assuming, for the present, that a body is composed of a number of atoms held together by their attraction for eacb< 

 other, it may be interesting to consider some facts in reference to the divisibility to which a body may be subjected 

 without losing its general and individual properties. The examples of such instances are so numerous as to make a 

 selection most difficult. The following, however, may be adduced, on account of their recent discovery : 



Example 1. In a cubic inch of chalk, as obtained from the rock, there are the remains of many millions of ani- 

 malcules, each of which had possessed, during life, all the organs necessary to its independent existence. 



Example 2. It has been found that silver exists in a soluble state in sea- water ; but in such minute quantities as 

 to liave escaped the notice of the most careful analysts, till lately, when a small portion of the solid metal was disco- 

 vered as a film on the coppered bottom of a vessel, and had been collected from the immense quantity of water 

 through which the ship had sailed during a long voyage. 



The extension of metals by hammering, and in the processes of wire-drawing, are familiar illustrations of a similar 

 nature. 



EXTENSION. This term, in its philosophical sense, defines that property of matter by which it occupies space ; 

 and, as it appears at once so evidently a quality of bodies, we pass on to another property, Impenetrability, which ia 

 not so self-evident, when considered in certain aspects. 



IMPENETRABILITY. By this is meant that no two bodies can occupy the same space at the same time. There 

 are many apparent exceptions to this, which, however, neither have, nor can have, any foundation in fact. Thus, on 

 adding strong sulphuric acid to cold water, in a long glass vessel, the two liquids, on being mixed, will occupy less 

 space than they did separately. This fact is, however, easily explained. No state of matter is really solid ; for 

 each mass has its atoms at a distance from each other ; the divisions between them being called pores or interstices. 

 In the instance just adduced, the particles are brought closer to each other, so that whilst the mass may occupy less 

 space, the individual atoms are impenetrable, or, in other words, could not at the same time occupy each other's 

 place. India-rubber, cork, atmospheric air, cfec. , all seem to create paradoxes in reference to this doctrine ; which, 

 however, are easily explained away, and on which further remarks will be made under the head of Cohesive 

 Attraction. Familiar instances illustrate the impenetrability of solids ; such as the insertion of a nail, chisel, or 

 saw into wood, <fec., where the particles of the wood are merely thrust aside, to make way for the body introduced 

 between them. 



INERTIA. That no inanimate mass can be set in motion spontaneously, will be readily admitted ; its converse, 

 that no body can come to rest spontaneously, may, however, be difficult to understand, owing to daily occurrences 

 seeming to demonstrate the opposite conclusion. A little consideration, however, will easily remove any doubts on 

 these two doctrines of the Inertia, or the immovability of matter. All matter requires the application of external 

 force to remove it from its position ; and so far as terrestrial objects are concerned, any force so applied is instantly 

 opposed in most cases by two others namely, those of gravitation and resistance. Taking, for instance, an extreme 

 case of motion such as the flight of a bullet from the muzzle of a rifle it is found that the ball instantly falls towards 

 the earth by virtue of gravitative force, and it is also diverted right or left, or opposed in its forward progress, by 

 the resistance of the air to its passage. The former of these forces may be temporarily suspended, as in the case of 

 a balloon ; tho latter as in the vacuum of an air-pump, wherein a penny and a feather will, owing to the absence of 

 air, descend at equal speed. 



With respect to the heavenly bodies, it is found that their rate of motion is so regular as to never vary in the 

 course of many years ; and thus they illustrate the second principle of the doctrine of Inertia that bodies will not 

 come to rest of thoir own accord. Occasionally, however, the proximity of one planet to another will disturb each 

 in its orbit. An instance of this occurred some years ago, which led to the discovery of the planet Neptune. 

 M. Leverrier, in France, and Mr. Adams, of Cambridge, had noticed a disturbance of the motion of Uranus, and 

 argriing on the principle that the inertia of that planet could not be affected except by an external force, they were 

 led to imagine that another planet had, by rirtue of its attraction, been the disturbing cause ; and, eventually, 

 they were rewarded by its discovery. This result may be adduced as a wonderful triumph of Mathematical and 

 Physical Science, and also as an evidence of the exact and undeviating character of natural laws, in obedience to 

 which, the planetary systems present no notable change in the lapse even of ages. 



