BOSCOVICHS THEORY. 



165 



B<J5co-.'ich's 

 theory of 

 Natural 

 Philoso- 

 phy. 



Applica- 

 tion of the 

 theory to 

 physics. 



Impenetra- 

 bility. 



Piati 

 LXV. 

 Si*. I. 



same absolute velocity takes place in all fluids, is mat- 

 ter of experiment. But we shall now proceed to the 

 application to physics ; what has been already said re- 

 specting mechanics, being a specimen of the bound, 

 less fertility of the field before us. / 



Application of the Theory to Physics. 



In treating of the application of the theory to me. 

 chanics, we have noticed many things connected with 

 the department on v^hich we are about to enter. But, 

 in order to proceed with more regularity, we shall re- 

 turn, in this place, to the general properties of bo- 

 dies, and, in afterwards proceeding to those particu-- 

 lar properties by which the variety of nature is ex- 

 plained, content ourselves with the deduction of the 

 common principles on which their respective proper- 

 ties depend. 



The impenetrability of bodies flows naturally from 

 the. theory of repulsive forces acting in the smallest 

 distances, the mutual compenetration of the points 

 being thereby prevented. Besides, as the least part 

 of space is infinitely divisible, whilst the number of 

 points of matter in any body is finite, it is infinitely 

 improbable that any two points should ever meet ; 

 *eeing there can be an infinite number of lines for 

 them to move in, besides that which joins them. If, 

 indeed, there were no repulsive forces, every mass 

 would pass freely through every other, as light 

 through glass, &c. and yet without any real compe- 

 netration ; but the forces extending to some distance, 

 hinder this free passage. Now, the curve of forces 

 may have no asymptotic arch, except the first DE, 

 in Fig. 1. of which the asymptote is in the begin- 

 ning of the abscisses. Or it may have several such 

 arcs. In this second case, if there be any asymptote 

 at a distance from the beginning of abscisses, which 

 has a repulsive arc without it, and an attractive arc 

 within, then the points placed at a nearer distance 

 cannot pass outwards, nor those at a greater distance 

 come nearer. And in this way we may conceive a 

 particle, a sheet, or a wall, composed of such points 

 which would be altogether impenetrable by any ex- 

 ternal force. But in the first case, where there is no 

 asymptotic arc except the first, it is plain, that if 

 a.velocity sufficiently great be given to any mass, it 

 may pass through any other without any derange- 

 ment of parts. For a certain time is requisite, in or- 

 der that the forces, by their action, may produce 

 any the smallest motion ; and we may suppose this 

 time by the swiftness of the motion to be diminished 

 without limit. Thus, an iron ball may pass swiftly 

 near several strong magnets, without being sensibly 

 attracted by them, although its passage might be al- 

 together prevented if it should move more slowly. 

 Should the motion of the ball be not 60 great, it 

 ;nay derange some of the nearest magnets, and even 

 carry them away with it, although the others at a 

 greater distance be not sensibly affected. Thus, a 

 ball from a gun passes through a plank of wood 

 without deranging any part but that which lies bc- 

 .ore it, though it would break all the neighbouring 

 parts if its motion were slower. And it is probably 

 '.he vast velocity of light which carries it througn 



pellucid homogeneous space without any compene- BoscovicV* 

 tration or derangement of its rectilineal motion. ^ let>r ^ 1 



From impenetrability arises physical extension : i,|',;| oso _ 

 For, since the points of matter cannot occupy the p hy. 

 same place, they must necessarily be posited without -v- ' 

 each other ; "and since they cannot be in absolute Extension. 

 contact, they must be separated by some space, how- 

 ever small, not all in one line or plane, but diffused 

 in space, extended in length, breadth, and depth, al- 

 though so near each other that the interval escapes 

 our senses. 



From extension arises figurability, since the space Figure, 

 throughout which the points are dispersed has its 

 limits, upon which its figure depends. The figure, 

 however, of those bodies which fall under our notice 

 can never be accurately defined, on account of the 

 inequalities of all surfaces ; but we take, in a vague 

 and indistinct way, that figure which seems to ap- 

 proach nearest to the true form. Thus, we say the 

 world is a globe, or a flattened spheroid, although 

 the roughness of its surface makes it very different 

 indeed from either the one or the other. From fi- Bulk* - 

 gure arises bulk, which is nothing more than the 

 whole space in length, breadth, and thickness, which 

 isjnclosed within the external surface, and therefore 

 our idea of it must be equally vague with that of the 

 figure. The mass of a body is the whole quantity Mast. 

 or matter, or, according to Boscovich, the number 

 of points belonging to it. Our ideas of mass are 

 yet more vague and indeterminate than those of bulk 

 or figure ; for it is not clear what must be excluded 

 when we take only the matter belonging to a body. 

 For all bodies are composed of very heterogeneous 

 parts, as is evident from ocular inspection, as well as 

 chemical analysis. Some exclude from the mass of 

 bodies that very fine ether, much rarer than air, 

 which they suppose interspersed throughout space ; 

 and even the air which occupies the pores of most 

 bodies, is considered as forming no part of them. 

 The water and air are no part of the spunge ; but 

 who considers the blood and juices as forming no 

 part of the animal, or the sap as no part of the living 

 tree : And air has been shown to exist fixed in many, 

 bodies, and essentially contributing to their constitu- 

 tion and properties. It is evident, therefore, that 

 our notion of the mass of a body is, as yet, but arbU 

 trary and rude. 



Density, is the relation of the bulk to the mass, Density. 

 and is greater when the mass is greater in the same 

 bulk. Hence the measure of density is the mass di- 

 vided by the bulk. But this theory differs from the 

 common opinion, as we have already seen, in suppo- 

 sing that there can be no limit to the density of bo- 

 dies, since the points of matter may approach to . 

 each other indefinitely near, or may be removed to 

 an indefinite distance. 



The inertia of bodies arises from the inertia of the Inertia.- 

 points, and their mutual forces : For having demon- 

 strated, that the centre of gravity of any system ie 

 either at rest, or moves uniformly in a straight line, 

 undisturbed by the mutual action of the points com- 

 posing the system ; it is plain, that the same thing 

 must take place in all bodies ; and the vis inertia: 

 consists in nothing else being the determination of. 



