218

CHAP. III.

Of the Physical Cause of Cohesion.

NSTEAD of setting out here with recount

ing all the minute phænomena of capillary tubes, sponges, drops of quicksilver, &c. &c. which have all been enlisted as so many undeniable proofs of an attraction of cohesion; though Sir Isaac Newton himself, more modest with all his knowledge than some who have retailed his doctrines to us, proposes none of these with any thing more than a suspicion or a conjecture concerning them; and some of them, as I could easily shew, have not been fairly reported or sufficiently inspected; I desire it may be considered-all the evidence of this sort is negative, and owes its whole worth to an arbitrary supposition, that the air is the only mechanical agent in nature; and that, merely through the want of another, we must have recourse to immaterial qualities, exerted by the particles of the bodies themselves, there

Of the Physical Cause of Cohesion. 219

*

being nothing else to which these effects can be ascribed.

>

To all this I oppose the following positive. matter of fact, worth an hundred little critical experiments, concerning which much may be said on both sides, while very little is understood on either. It is this-Nature is provided with the element of fire, a material agent of sufficient force and subtilty to overcome and undo the strongest effects vulgarly ascribed to cohesion. And as the design of our infinitely wise and bountiful Creator in appointing a material agency, was to build up rather than destroy, to promote and preserve an orderly disposition in bodies, at least as much or more than to cause their dissolution; it is evident to reason, the same agent, acting with some difference of condition and circumstances, must be sufficient to do both. The air, when stirred into a tempest, will tear an oak up by the roots; but was this the sole end of its creation? Does not the same air assist the oak and all other trees in their growth? and does it not nourish and preserve many more than it destroys?

Fire,

See Mr. Rowning's account of the capillary tube, in the Preface to his System of Philosophy.

Fire, another element, hath in like manner its different offices; and we may hope to gain some light into its more secret operations, if we argue by analogy from one of these to the other. That fire is the great catholic dissolvent of nature, the chymists have all been ready enough to confess; that it can unite, as well as separate, ought not to be doubted; though it is what few will believe, unless they are possessed of patience and perseverance enough to go through a close inquiry. However, this matter is not so very difficult as they may apprehend.

Let us consider this agent a while in the first and best known of its capacities, I mean as a dissolvent. The particles of mercury, from the sphericity of its drops, should seem to be endued with a strong attraction: yet these particles will cease to have any cohesion, and be separated into fumes by a degree of heat but little exceeding that of boiling water. The particles of water are also said to be endued with the like virtue: yet the agency of fire will very soon relax their cohesion, as appears by a sensible diminution of their specific gravity. The same fire acting with a still greater degree of force, will at length totally dissolve their

union, and raise them aloft in steam or vapour. The ordinary heat of the sun has a like effect on the waters of the ocean. All other substances, as well solid as fluid, are subject to a separation of their parts by the entrance of fire: the hardest of metals, how closely soever their parts may be connected, are easily dissolved and rendered fluid by the heat of a furnace,

Conlabefactatus rigor auri solvitur æstu,

If nature then is provided by its author with an element of such power and activity as enables it to overcome the strongest cohesions, it cannot be destitute of an agent powerful enough to cause them: if it can do the greater, it must certainly be able to do the lesser. And without much disputing, do we not find it to be thus in fact? For the æther, acting below a certain degree, will consolidate the particle of water into ice: if it acts above that degree, it keeps the water fluid: if to an higher degree, it renders it more fluid if to an higher still, a total separation of the parts will ensue. But if

:

these parts mount up into the head of an alembic, where the action of the fire is different, they are united again into a well

connected

connected body. These effects being answerable in every instance to the activity and condition of a material agent, what necessity is there for calling in the assistance. of an unmechanical attraction? the work may certainly be done without it*; and I am verily persuaded such a principle would never have been seriously defended, if the agency of fire had been searched into as it deserves. If I can see the effects vary as oft as there is any change in the element of fire, I am compelled, by all the rules of reason and philosophy, to understand this element as an immediate cause of these effects, and must receive it as such, till it is demonstrated to be inadequate; the contrary to which hath been demonstrated already, and might be farther confirmed by some other experiments, which I might here introduce, if there were any occasion for them.

The cohesion of bodies by the action of this fluid, may be illustrated and confirmed in a familiar way by some parallel effects, in the explication of which we are all agreed. Let a stop-cock be fastened to the neck of a bladder, that it may be screwed upon the

work

*Entia non sunt multiplicanda absque necessitate.