NATURAL PHILOSOPHY-MATTER, MOTION 



AND HEAT. 



AS man contemplates the bodies that make up 

 the universe, and the endless movements 

 and changes they undergo, he becomes impressed 

 with the conviction that these phenomena (appear- 

 ances), as they are called, are not simply a collec- 

 tion of individual things ruled by chance, but that 

 there are fixed connections in other words, order 

 and uniformity among them ; and he feels irresist- 

 ibly impelled to trace out these connections, or 

 laws of nature, as they are called, wherever they 

 can be discovered. In this pursuit we have Natural 

 Philosophy in its widest sense. 



Some phenomena depend upon the peculiar 

 kind of substance of which the body manifesting 

 them is composed, and consist in changes of its 

 constitution. The facts of this class form the 

 separate science of Chemistry. Organised bodies 

 that is, plants and animals also manifest a 

 peculiar set of appearances which are summed up 

 in the word life. The consideration of vital phe- 

 nomena belongs to the department of science 

 called Physiology, sometimes Biology. 



But there is a large and important class of 

 phenomena of a much less special kind, and which 

 belong to matter in general, and to all bodies 

 composed of it, whatever be their peculiar con- 

 stitution, and whether organic or inorganic. Thus, 

 a stone, a piece of sulphur, a drop of water, a 

 plant, an animal, all fall to the earth if unsup- 

 ported, are all capable of being divided into small 

 parts, all reflect more or less light, &c. It is the 

 investigation of universal laws of this kind, where 

 no change of constitution is concerned, that con- 

 stitutes Natural Philosophy, in its narrower sense ; 

 for which the term Physics is now more generally 

 used, as being more precise. Of those physical 

 phenomena, again, some have a higher generality 

 than others, and it is these most general laws ef 

 the material world that naturally fall to be dis- 

 cussed in this introductory treatise. They may 

 be arranged under the heads of General Properties 

 of Matter, Motion and Forces, and Heat. 



GENERAL PROPERTIES OF MATTER. 



Matter, or that which composes all bodies, has 

 certain properties j by which is meant, that it has 

 the power of making certain impressions upon our 

 senses, or of exciting in us sensations. As to what 

 matter is in itself, beyond its power of affecting our 

 senses, we know nothing. The something, what- 

 ever it is, in which this power is conceived to reside, 

 is called substance. Some philosophers deny the 

 existence of anything beyond the properties. So 

 far as natural science is affected, the question is of 

 no moment ; what really concerns us is, how matter 

 appears and acts, and not what it is. The more 

 important of the properties of matter are Im- 

 penetrability, Extension, Divisibility, Indestructi- 

 bility, Inertia, Porosity, Compressibility, Elas- 

 ticity, Attraction, States of Aggregation, Mallea- 

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bility. We shall describe and illustrate them 

 in succession, classing such qualities together as 

 seem to be naturally connected. 



Impenetrability is that quality of bodies by 

 virtue of which each occupies a certain portion of 

 space, to the exclusion of all other bodies it 

 expresses the fact that two bodies cannot be in 

 the same place at the same time. In the popular 

 sense of the word, matter is anything but impene- 

 trable. The hand can be thrust into water, a nail 

 can be driven into wood. But all these are instances 

 merely of displacement. That the most mov- 

 able and unsubstantial substances, when displace- 

 ment is prevented, occupy space as effectually as 

 the most solid, is seen in a blown bladder, or in 

 an air-cushion. This property of air is taken 

 advantage of in the diving-bell. 



Extension or Magnitude, and Form. Mag- 

 nitude or size is one of those simple ideas that do 

 not require or admit of explanation, because there 

 is nothing simpler to explain them by. It is 

 chiefly by their extension that bodies make them- 

 selves known to our senses. 



Divisibility. There is no known limit to the 

 divisibility of matter. A chip of marble may be 

 broken from a block, and that chip may be 

 crushed to powder. The smallest particle of this 

 powder discernible by the naked eye, when ex- 

 amined by the microscope, is seen to be a block 

 having all the qualities of the original marble, and 

 capable, by finer instruments, of being divided 

 into still smaller blocks, which may be again 

 divided ; and so on, with no other limit than the 

 fineness of our senses and instruments. 



The unlimited degree to which matter may be 

 comminuted is yet more strikingly seen in other 

 ways. When a substance is dissolved in a liquid, 

 or water rises in vapour, the particles become so 

 minute as to be invisible with the most powerful 

 magnifiers. The microscope, again, has revealed 

 the existence of animals, a million of which would 

 not occupy more space than a grain of sand. Yet 

 these animalcules, as they are called, have limbs 

 and organs, and display all the appearances of 

 vitality. How shall we conceive the smallness of 

 the tubes or vessels in which their fluids circulate, 

 and the minuteness of the particles of matter 

 composing these tubes and fluids ! 



Divisibility thus extends far beyond the limits 

 perceptible to the senses. Are we, therefore, to 

 assume that it is without limits that matter is 

 infinitely divisible? This would be a rash as- 

 sumption. On the contrary, there are many 

 reasons for believing that there is a limit some- 

 where, and that there are ultimate particles, of a 

 determinate size and shape, incapable of further 

 subdivision. These assumed ultimate particles 

 are called atoms, from a Greek word signifying 

 indivisible. Their existence is inferred from a 

 number of facts connected chiefly with crystallisa- 

 tion and chemical combination, which cannot be 

 otherwise explained. These ultimate particles or 

 atoms, it is assumed, first form definite groups, 



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