444 THOUGHTS ON THE 



having been shaken, exude by its natural gravity through 

 apertures and crevices if they be somewhat minute. It is 

 evident then that there is a tendency to continuity in fluids 

 also, but weak. On the contrary, however, it is strong in 

 solids, and predominates over the natural motion, or that 

 of gravity. For if any one conceives that in a pillar of 

 wood or stone, the upper parts do not throughout affect 

 descent, but rather to maintain themselves in entirely the 

 same position, he will easily set himself right, by consider 

 ing that a column or similar structure, if the altitude is 

 disproportioned to the base, or exceeds the due relation to 

 it, cannot stand, but is precipitated by its own gravity. 

 So that in very elevated piles of building it is necessary to 

 make them incline to the pyramidal form, and narrow to 

 an apex. What that principle in nature is, however, which 

 determines the intensity or weakness of the affection of 

 continuity, will not easily occur to the inquirer. It might 

 perhaps be suggested that the parts of solids are more con 

 centrated and compact, those of liquids more lax, or that 

 in liquids there was an ether, the principle of fluidity, which 

 was wanting in solids and the like. But neither of these 

 explanations is reconcileable to truth ; for it is apparent 

 that snow and wax, which can be divided, cast into form, 

 and receive the impression of other bodies, are a much 

 rarer substance than melted quicksilver or lead; as is 

 proved by a comparison of their weight. But if any one 

 still insists that it is possible that snow or wax, though (as 

 a whole) less gross than quicksilver, may nevertheless have 

 its parts disposed more closely and compactly, yet that as 

 it is a porous body, containing many cavities and much 

 air, it is therefore rendered lighter as a whole: as is the 

 case of pumicestone, which, though in comparing the size 

 of both, it be perhaps lighter than wood, nevertheless if 

 both be ground to a dust, the dust of the pumicestone will 

 outweigh that of the wood, because the porosity of the 

 former no longer continues : these are well observed and 

 well objected facts. But what shall be said of melted 

 snow or wax, where the same interstices are now filled up : 

 or what of gum mastick and the like substances, which 

 have no perceptible cavities of the kind, and are yet lighter 

 than several liquids ? As to the allegation of an ether by 

 the virtue and impulse of which things are put into the 

 state of being fluid, that, no doubt, is at the first glance 

 probable, and falls in kindly with the common notions: but 

 in the experience of actual nature, it is much more hard to 



