170 Nc-iu Theoiy of the Conjlitui'ion 



themfelres according to their fptcific gravity." Now, as I 

 am peiTitaded lliat no one acquainted with the principles of 

 mechanical philol'ophy could have written the above if he 

 had underftood my hypothefis, it feems to call from me a 

 further explanation. I propofe therefore, id. To Hate, in as 

 clear a point of view as the fubjccl will admit, the principles 

 which I affiuiie : 2d, To fliow that the conftqucnccs which I 

 have deduced from them are legitimate ; and, particularly, that 

 mixed elaftic fluids ought not to arrange themfelves according 

 to their Ipccific gravity : and, 3d, To dcmonftrate that the 

 fuppofition of the gafes conftituting the atmofphere being 

 held in a ftate of equal difl'ufion by chemical affinity, is not 

 only inconfiftent with the phenomena, but is completely 

 abfurd. 



T. Frinciples ajjumed. 



1. T take for granted, that the particles of fimple [un- 

 mixed] elaftic fluids repel one another with forces inverfely 

 as the diftance of their centres, the temperature being given. 

 This is a mathematical deduction from the allowed faft, that 

 the fpace occupied bv any gas is inverfelv as the compreffing 

 force. (See Newton's Pr'nicipia, b. ii. prop. 23,) The ah- 



folule dillances of the centres of fuch particles muft vary ac- 

 cording to circumftances, and cannot erjily he determined ; 

 their relative diftanccs in a liquid and aerial ftate fomctimes 

 may. Mr. Watt has fiiown tliat fieam of 212°, and preftiife 

 28 inches, is 1800 times lighter than water; confequenlly 

 the diftanccs of the particles of ftcam arc to the diftances of 

 the faid particles in a liquid ftate as 13 to i, nearly, in that 

 particular cafe. Vapour in the vacuum of an air-pump, at 

 common temperature, will have its particles about lour tiiBes 

 the diftance, or 48 to i. 



2. I fuppofe that in mixed elafiic fluids the heterogeneous 

 particles do not repel one another at all at fuch diftances as 

 they repel thofc of their own kind ; but that fuch panicles, 

 vhcn brought into aftual cbntaft (to ufe the common lan- 

 guage), refift each other in all refpe<Sts like inelaftic bodies. 

 Thii is the peculiarity of the hvpotliefis, and what appears 

 not to be generally undf^rftood. jf I may explain by analogy, 

 the mod ftrikint^ will be found in magiietifm. Two like 

 poles of magnets repel one another with the fame force, whe- 

 ther anv other bodies intervene or not, and do not afl'cft thc)le 

 other bodies: in the fame way I conceive two particles of any 

 one sras repel one another with the fame force, whether par- 

 ticles^of other gafes intervene or not, and do not afi'eft tho<'c 

 other particles. A magnet is auicuablc to the conunon laws 



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