204 VARIATIONS OF COHESION. 



vigour, increasing inversely as the squares of the 

 distances from their centres of action. 



Even admitting that moisture floats in the atmo- 

 sphere to the highest elevation at which that is esti- 

 mated to have sensible weight, which is about fifty 

 miles above the mean surface, that is only one-eigh- 

 tieth part of the distance of the mean surface from 

 the centre, so that, from mere gravitation alone, the 

 same quantity of water, when it reaches the surface, 

 will have only about one-fourth more gravitation 

 than it would have at the height of fifty miles. 



It is very different with the cohesion, or, as it is 

 called, when the substances are not touching each 

 other, the attraction of cohesion, because the centre 

 of that is in the body itself; so that, whenever from 

 any cause, and that cause may be generally, if not 

 invariably, said to be a cooling, or suspension of 

 heat, the moisture in any part of the air becomes 

 more dense than that in the surrounding parts, the 

 centre of that part instantly becomes a centre of co- 

 hesion ; and those particles of water which are situ- 

 ated at half the distance have four times as much ten- 

 dency towards that centre, and so on for all other 

 distances. 



Thus we see that the tendency of moisture in the 

 air to form a cloud is much greater than the tend- 

 ency of that cloud to fall after it is formed ; and 

 that it is so without reference to any thing else than 

 the three principles of gravitation, cohesion, and 

 heat, principles which, in themselves, contain the 

 abstract of the whole philosophy of matter. It is 

 not unusual to call in at this stage of the business 

 the assistance of ideal causes, much after the same 

 fashion as those who know not the true God wor- 

 ship idols, or those who are ignorant of the truth 

 give currency to any untruths ; but the careful ob- 

 server of nature should be especially on his guard 

 against false causes ; for it is in them* that all error 

 in the knowledge of nature lies. It has not been 



