68 



ON THE PROPERTIES OF MATTER, 



more so: and it is this kind of attraction which is called the attraction of 

 ag-gregation. And in both these cases the attraction in question evinces a 

 considerable superiority of force to the general attraction of gravitation; 

 since the particles of the drops or globules ascend from the surface of the 

 glass, except those that form their narrow base, and are drawn towards their 

 proper centres, instead of being- drawn towards the centre of the earth. 



If, however, the convex shape of the drop of water be destroyed by pressing 

 it over the glass into a thin extended film, the general attraction of gravitation, 

 acting with increased effect upon an increased space, will overpower the indi- 

 vidual attraction of aggregation, and the particles of water will be restrained 

 from attempting a spherical figure as before. In the quicksilver, nevertheless, 

 the attraction of aggregation being much stronger than in the water, it will 

 still continue to prevail ; and it is only by a very minute and elaborate divi- 

 sion of the particles of this material that we can give to the attraction of ' 

 gravitation a predominancy. 



The same result occurs in the homogeneous particles of oil. And hence, 

 if we divide its particles by shaking a certain portion of it in water, we find, 

 upon giving the mixture rest, that the water will first sink to the bottom, or, 

 which is the same thing, the particles of the oil will rise to the surface ; and 

 then that these particles, as soon as they have reached the range of each 

 other's attraction, will unite into one common body. 



Now, in ail these cases it is obvious that the particles of matter thus 

 obeying the law of homogeneous attraction assume or attempt to assume a 

 spherical figure ; and we not unfrequently perceive a similar attempt, even 

 where the breadth of the surface, and the consequent potency of the attraction 

 of gravitation, would hardly induce us to expect that there could be the least 

 effort towards it: as, for example, in a glass brim-full, or somewhat more 

 than brim-full of wine, or any other liquid. 



We behold the same figure in the drops of rain as they descend from the 

 clouds ; a figure which, in fact, is the sole cause of the vaulted form of the 

 rainbow, as I may possibly take leave to explain more particularly on some 

 future occasion. We behold it in reality throughout all nature, in every sub- 

 stance whose particles are capable of uniting and separating with ease ; and, 

 consequently, of readily obeying the laws of cohesibility and divisibility, as 

 those of liquids ; and we should see it equally in solids, but that the particles 

 of these last are incapable of doing readily either the one or the other. 



What, then, is the general cause that produces so general an effect ? 

 Clearly this : a cause to which I have already in some degree adverted, in 

 speaking of the general attraction of gravitation : that, there being an equal ten- 

 dency in every particle of homogeneous bodies to press together, they must 

 press equally towards one common centre, and strive to be as little remote from 

 that centre as possible. Such a strife, however, must necessarily produce a 

 globular or spherical form; for it is in such a form only that the extreme par- 

 ticles, or those constituting its surface, and which are prevented from a closer 

 approach by those that lie within, are equally near and equally remote in 

 every direction. 



Hence, then, the cause of the globular figure of drops of quicksilver, drops 

 of water, drops of rain, and drops of dew, collected and suspended from the 

 fresh leaves of plants in the balmy air of the morning : and hence one reason, 

 though there is also another that concurs with it, and which I shall explain 

 presently, for the convex shape assumed by a wine-glass of liquid of any * 

 kind, on its surface, when brim-full, or somewhat more. 



The same reasoning may be applied to account for the spherical figure of 

 the heavenly bodies ; each of which, though probably composed of many 

 difl:erent or heterogenous substances in itself, may be fairly contemplated as 

 a homogeneous mass when compared with those by which it is surrounded : 

 and hence, too, we see the necessity for their having at first existed, from 

 some cause or other, in a fluid state ; since, otherwise, the different corpuscles 

 which enter into their make could not have assumed that symmetrical 

 arrangement which alone gives sphericity to the total bulk. 



We have equal proofs of the same peculiar attraction existing between 



