4S 



ON THE PROPERTIES OF MATTER, 



question evinces a considerable superiority of force to the general altractioii 

 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 press- 

 ing it over the glass into a thin extended film, the general attraction of gra- 

 vitation, acting with increased effect upon an increased space, will over- 

 power the individual 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 division 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 all 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 

 substance 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 parti- 

 cles 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 efl^ect ? 

 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 tendency in every particle of homogeneous bodies to press together, 

 they must press equaMy 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 particles, 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 apphed to account for the spherical figure 

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



