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Show I ., f . 204 VARIATIONS OF COHESION. via-our increasing inversely as the squares of the 0 ' • distances from their centres of actwn. Even admitting that moisture floCl:ts in the. atm~sphere to the highest elevation at w~nch. that IS estimated to have sensible weight, whtch ts about ~fty miles above the mean surface, that is only one-eightieth part of the distance of the mean surface from the centre, so that, from mere .gravitation alone, the same quantity of water, when 1t reaches the st~rfa~e, will have only about one-f?urth more ~avitatwn than it would have at the height of tifty miles. . . It is very different with the cohesiOn, or~ as 1t lS called when the substances are not touchmg each other 'the attraction of cohesion, because the centre of th~t is in the body itself; so that, whenever. from any cause, and that cause may be generally, .If not invariably, said to be a coolmg, or suspensiOn of heat, the moisture in any part of th~ au becomes more dense than that in the surroundmg parts, the centre of that part instantly becomes a c.entre of .cohesion ; and those particles of wat~r which are situated at half the distance have four ttmes as much tendency towards that centre, and so on for all other distances. . · h Thus we see that the tendency of mmsture In t e air to form a cloud is much gre~te~ than the tendency of that cloud to fall after It 1s ~ormed; and that it is so without reference. to ?-DY thmg e.lse than the three principles. of ~ravttatwn, cohesw~, and heat,-principles which, m themselves, contam t~e abstract of the whole philosophy of matter. . It IS not unusual to call in at this stage of the busmess the assistance of ideal causes, much after the same fa~hion as those who know not the true God worship ido1s, or those who are ignorant of the truth give currency to any untruths; bu~ the car~ful observer of nature should ~e. e~pecmlly on his guard against false causes · for It IS In them that all error in the knowled~e ~f nature lies. It has not been - _, .. PIIIJ.OSOPHISTIC IDOLS. 205 unusu~l. to delegate the process of cloud-making to electricity, to magnetism, and to the aurora borealis; but in all p~obability, though there may bP- other and accompanymg appearances of those states of the atmosphere that prece~e or accompany rain, we have ~o more reason to beheve that they are primary or active a.gents than .we have for believing that a Lapland ~vncl~ can rmse wind, or fairies prauk tha sward With Circles. Those last-mentioned causes w~re once i~ ~s high repute as any of the witch and fa1ry superstitiOns of philosophy; and thouO'h those who know better have discarded the witch::> and the fairy, there are people who still bow down to the other idols. Electricity, and the other supposed disturbing causes of the atmosphere that have been mentioned are mere appearances which matter under circum~ stances, some of which we do and some we do not understand, puts on; and as it is contrary to the whole tenor of our observation to believe that a mere appearance can act, in any way whatever, we should treat those appeara!lces as sensible people treat all appearances-that 1s, we should say nothinoabo. ut them which we do not understand. Tha~ which we call a substance, or matter, is not mere ~lJ~pear~nce, or even an accumulation of appearances, 11_ 1~ an 1.nfere~1ce from those appearances and the relatiOns m whiCh we observe them; and as that inference and ~he perception of those relations, are acts of the mmd subse9.uent upon observation by the s~nses, ~e m~y conJecture and speak of it, and make d1scovenes wtth regard to them by the mind only, even though all our senses should become obliterated ; but with regard to mere appearances they can be known only through the medium of the senses· and ~eyond observation every attempt is an error: Nor 1~ t~ere any necessity for inventing new powers or prmciples, for the three that have been statecl ue perfectlv sufficient to produce every appearanc~ s |