60 ON THE PROPERTIES OF MATTER, 



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 be- 

 come more pliable to the action of water or of any other liquid 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 overpowered ; and as- 

 cends from the surface of the earth, instead of descending to it, or uniting 

 into a spherical form ; and tbe same kind of pores, and, consequently, the same 

 kind of power, being continued to the utmost height of the sponge, it will 

 rise to the full extent of its column. The tubes of various imperfect crys- 

 tals, 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 becomes dissolved, and, 

 consequently, its pores" are totally destroyed. The cause of capillary attrac- 

 tion is therefore obvious : and the reasoning and phenomena now submitted 

 may be applied to an explanation 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 they have 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 off 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 pecu- 

 liar modification of that of gravitation, more select in its range, but more 

 active in its power. To trace out the various substances that are pos- 

 sessed of this peculiar property, and to measure the degrees of their affini- 

 ties, is one of the chief branches of chemistry, but of too voluminous a 

 nature to touch farther upon at present. 



IV. V. The two remaining kinds of attraction to which I have adverted, 

 those of ELECTRICITY and of MAGNETISM, are still more select, and perhaps 

 still more powerful than even the preceding : but the phenomena to which 

 they give rise cannot, I think, be attributed to any modification of a gravi- 

 tating ethereal medium. We call the medium in -both these cases a fluid, but 

 we know little or nothing of the laws by which they are regulated ; whether 

 they be different substances, or, according to M. Ampore, the same substance 

 under different modifications, or whether, in reality, they be material sub- 

 stances at all. They are certainly deficient in the most obvious properties 

 of common matter, and may be another substrate of being united to it. 



There are also two other substances, or which are generally conceived to 

 be substances, in nature, of a very attenuate texture, which largely con- 

 tribute to the changes of material bodies. I mean LIGHT and HEAT, of the 

 general nature of which we are still also in a considerable degree of igno- 

 rance. Like the powers of magnetism and electricity, we only know them, 

 and can only reason concerning them, by their effects. These effects, indeed, 

 are of a most curious and interesting character, but spread too widely to be 

 followed up in the course of the present lecture, though we may endeavour to 

 pursue them, and, as far as we are able, to develope them, hereafter. 



All these four powers or essences, for we know not which to call them, con- 

 cur in exhibiting none of the common properties of matter ; their respective par- 

 ticles repel each other at least as powerfully as they attract, and in the cases 

 of light and heat repel alone, and without attracting. They may, possibly, 

 be ponderable ; but if so, we have no instruments fine enough to detect their 



