50 THE PROPERTIES OF MATTER j 



HETEROGENEOUS ATTRACTION, and, ffom its occurring most palpably be-* 

 tween liquids and solid substances possessing small capillary or hair-tubes, 



CAPILLARY ATTRACTION. 



The cause of this attraction is obvious ; and it is still more clearly a 

 mere modification of the general attraction of gravitation, than the pre- 

 ceding power of homogeneous attraction. It is the common attractive 

 property of material substance for material substance ; the Hquid, or that 

 whose particles are easily separable, pressing towards the solid, whose 

 parts are by any action of their own altogether inseparable. Hence the 

 reason why water or any other liquid hangs about the sides of a wine- 

 glass : hence, partly, the reason why a wine-glass, when somewhat more 

 than brimful of a liquid, does not overflow ; the co-operative reason 

 being, as I have already stated, the homogeneous attraction of the cor- 

 puscles of the fluid for each other, which prevents them from separating 

 readily ; and hence also the reason why a liquid contained in a narrow- 

 necked and inverted phial does not obey the common attraction of gravita- 

 tion, and fall to the earth, although the stopper be removed to allow it, till 

 we aid the power of gravitation, or rather loosen the power of the peculiar 

 attraction, by shaking the phial. 



In this last case it is manifest that the heterogeneous attraction, or that 

 between the two different substances, is stronger than the common force 

 of gravity. In minute capillary tubes or pores this is still more obvious. 

 Such are the pores of a piece of sponge, when pressed or softened, so as 

 to become more pliable to the action of water or of any other hquid 

 within its reach. For, in this case, the water being minutely divided by 

 the pores of the sponge into very small portions, and still surrounded by 

 the pores in every direction after such division, has its common force of 

 gravitation and its peculiar force of homogeneous attraction equally over- 

 powered ; and ascends from the surface of the earth, instead of descending 

 to it, or uniting into a spherical form ; and the same kind of pores, and, 

 consequently, the same kind of power, being continued to the upmost 

 height of the sponge, it will rise to the full extent of its column. The 

 tubes of various imperfect crystals, as those of sugar, for example, are 

 still smaller : and hence the lateral attraction must be still stronger ; and 

 any liquid within its reach will rise both higher and more freely, till the 

 sugar at length Ipecomes dissolved, and, consequently, its pores are fotally 

 destroyed. The cause of capillary attraction is therefore obvious ; and 

 the reasoning and phasnomena now submitted may be applied to an ex- 

 planation of every other species of the same kind that may occur to us. 



III. The third particular attraction I have noticed, is that of peculiar 

 BODIES FOR PECULIAR BODIES, and which has hence been denominated 

 ELECTIVE or CHEMICAL ATTRACTION ; as the tendencies theyliave to each 

 other have been denominated affinities. Thus lime has a strong affinity 

 for carbonic acid, and greedily attracts it from the atmosphere, which hence 

 becomes purified by being deprived of it^. But the same substance has a 

 still stronger affinity for sulphuric acid, and hence parts with its carbonic 

 acid, which flies oflf in the form of gas, in order to unite with the sulphuric 

 whenever it has a possibility of doing so. It is highly probable that this 

 kind of attraction is also nothing more than a peculiar modification of that 

 of gravitation, more select in its range, but more active in its power. To 

 trace out the various substances that are possessed of this pecuhar property, 

 and to measure the degrees of their affinities, is one of the chief branches 



