On the Expamion avd ConlraciiGn of IVaier. 55 



upon a hot iron. Haiiy* observes that this was the opi- 

 nion of Descartes, who thus endeavoured to account tor tlie 

 formation of the six radii which arc observed to form a 

 floccule of Pnow. But Descartes says, when treating on 

 the shape of the pirticles of water, " Dcinde f snppono 

 exignas illas partes, qinhiis aqua coniponitur, h)ngn.s, la;ves 

 et hibricas esse apiruil'arun) parvularuni ms-tar, &c.:" and 

 that they only assuuud the sh;ipe of a splicre when con- 

 verted into vapour, fr.)m the rapid motion into which they 

 are tlirown, in these words; '• Sed | conira quiim vaporis 

 formam habcnt, agitatio illarum adeo e<t concitata, ut ce- 

 lerrime rotentur in^onines partes, et cailem opera in longi- 

 tudinem suam porrignntur; unde fit ut singula?, illarum re- 

 hquas suis similes, irruptionem in parvas spl.oerulas, quas 

 describunt, molicntcs, arcere atque abigere possint, &c." 

 Hence he had recourse to this reasoninsj to actount for the 

 formation of t!ie radii already mentioned, as his theory re- 

 specting tlic particles of water could not be adapted to this 

 phcanomcnon, — But to return to our subject. 



Then, at the dcpree above mentioned, I would say that the 

 particles of water arc in contact only at certain points ; but 

 irom the caloric, gramini!; it to be a fluid, filling up the in- 

 terstices, their mutual affinity is prevented from acting so 

 forcibly as to change their figure. In illustration of this, 

 we may take a pile of balls, as a rough comparison, each 

 ball having for those around it a strong affinity, and which 

 are nrevenlcd irum acting upon each other, orrunnirrg into 

 a aoiitl luass, by sand or some substance being poured into 

 the various crevlc^ti, .which nevertheless does not prevent 

 their touching in certain p^nots. But as by the reduction 

 of temperature part of the caloriG i» withdrawn, which 

 being interspersed throughout the water, as just explained, 

 prevented these particles from afTecting each ()ther, the 

 affinity they exert amoi^g thcnjselves now begins to take 

 place, and their siuipe becomes altered from that of a sphere 

 to some other figure. Heuce, as a sphere contains the 

 greatest quantity "of matter under the least given super- 

 ficies, the superficial contents of these atums will be m- 

 crcased in proportion as they deviate from that form. 



Although they are thus enabltd to act upon each other, 

 still they attract around ihem a quantity of caloric, by 

 means of wiiich llity are kept so lar separate as to remain 



* Hii'iv'sNaUiral Philo-ophy; tr:jn». by Dr. O. Gregory. 



f lifii/ii Jci OuilusSjjeamtiia I'hiLjio^liUP' Amitelod tini, aailo cio iac Ixxii. 



I iLiJ. ' 



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