most strongly, whose touching surfaces are largest. 6. This power must decrease, as the squares of the distances increase; because it must be supposed to issue from each particle in right lined directions. 7. Where the sphere of attraction ends, there a repelling power begins; by which the particles, instead of attracting, repel and fly from each other. 8. By this power the small portions or drops of a fluid conform themselves to a spherical figure. The first and second of these properties are evident from various experiments; as the sudden union of two contiguous drops of mercury, water, &c; the strong adhesion of two leaden balls which touch by polished surfaces; as also of panes of glass and in capillary tubes; the rising of water by the sides of a glass vessel, and into tubes of sand, ashes, sugar, spunge, and all porous substances. The third property is proved by the sticking or adhering of water to substances, which by mercury are left dry. The fourth and fifth properties are evinced by the hyperbolic curve, formed by the superficies of a fluid ascending between glass panes touching each other on one side. The sixth property is evident. The seventh appears from the ascent of a steam, or vapour, from humid or fluid bodies; and the eighth property

H 4

property is manifest by drops of water falling on dust.

From this account of the attraction of cohesion, we have a rational solution of several very curious and surprizing phænomena; as why the parts of bodies adhere and stick so firmly together why some are hard, others soft; some fixed, others fluid; some elastic, others void of elasticity all which arise from the different figures of the particles, and the greater or less degree of attraction consequent thereupon. On this principle, we account for the manner in which plants imbibe the nutritive juices by the fibres of the roots; also for the rise of the sap in vegetables, and for the whole economy of vegetation. Hence the rationale of the various secretions of fluids by the glands, and their wonderful circulation through the fine capillary vessels. Hence also the reason of gilding metals; also of melting or fusion by heat. Hence also the exhalation of vapours by the heat of the sun or fire; the aggregation of aqueous particles in the air, forming the drops of rain. We hence see the reason of distillation, filtration, dissolution, digestion, sublimation, precipitation, crystallization, and the other operations of chy

mistry and pharmacy. Lastly, It is by the powers of attraction and repulsion that we are, in most instances, to account for those wonderful phænomena of subterraneous ascensions and explosions; of volcanos and earthquakes; of hot springs, damps, and suffocating exhalations in mines.

Notwithstanding these clear and satisfactory data, the cause of the cohesion of matter has extremely perplexed philosophers in all ages. In all their various systems of physics, matter is supposed, originally, to consist of minute divisible, or indivisible atoms; but how, and by what principle these several and distinct corpuscles should be first combined into little systems, and how these little systems should come to persevere in that state of union, is a point not yet determined a point of the greatest difficulty, and even of the greatest importance of any in physics. J. Bernouilli thinks it owing to the pressure of the atmosphere; others to the figure of the component particles; but the generality, with Sir Isaac Newton, to attraction.

The attraction of gravitation, though reckoned a distinct power from that of cohesion, yet, when well considered, may be found perhaps to

differ from it no otherwise, than as a whole from its parts for the gravity of large bodies may be only the result or aggregate of the particular powers of the constituent particles, which singly act only in contact and in small distances; but with their joint forces, in vast quantities, produce a mighty power, whose efficacy extends to very great distances, proportional to the magnitudes of the bodies.

This doctrine of the attraction of gravity, however ably supported by its illustrious patron, has had weighty difficulties thrown in its way. As all motion, it hath been observed, is in the direction of its cause, there can be no such thing as a power of attraction; because that supposes a direction in the cause, which is contrary to the direction of the effect, and therefore can never happen consistently with the laws of mechanism. A cause from the earth, can never bring the moon nearer the earth; neither can a cause from the moon bring the waters of the earth nearer to the moon. The cause which is in the direction of a body that moves freely, is an impelling cause; and if it be impulse, it is not attraction; if it be attraction, it is not impulse: these principles being of opposite natures, and consequently inconsistent.

In opposition to this, it has been contended, that attraction must be essential to the actual existence of all matter, since no substance can retain any form without it. Gravitation, says its advocates, is unquestionably one of the most simple laws, or principles of motion, which has been observed in the constitution of the universe. This, reply its opponents, is not to be denied. But, is the attraction given to it to be supported on sound and on rational principles? Gravitation from such premises, would seem to imply a law or a power in the active body; attraction in the passive one; and consequently, if the acting body should be made to move by its own gravity or weight, there would be no necessity for an attraction; or if it were to act by attraction, there would be no necessity for gravitation.

How inexplicable soever the cause of this gravity may be, it yet would appear from some of its admirers, who do not even qualify it with a doubt, as their master did, to be a mode of motion, a tendency towards a center. To speak strictly, a relative gravity is a relative quality; for what falls relatively to us, rises as relatively to other bodies. Hence, say they, it follows, that all motion in the universe is the effect of gravitation, seeing as we do, that in the universe there