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ASTRONOMICAL PAPERS. 



141 



4. Heat whlcli is produced, by inflammation feems alfo 

 to depend on the chymical mixture of bodies. In all bo- 

 dies which blaze there is found an acid and mephytic air, 

 which feem to abound in thofe bodies in proportion to their 

 different degrees of inflammability. The feparation of 

 thefe two bodies conftitutes a flame; this we oblerve can 

 only be efFeded by means of a third body, viz. common 

 air. The union of the acid with the w^ater that is fuf- 

 pended in the air, and the union of the mephytic with the 

 common air, produces two heating mixtures. Hence heat 

 is excited by flame. 



5. Heat is produced by the Sun : Docs that heat pro- 

 ceed immediately from the Sun, as is generally fuppofed, 

 or is it mechanically excited by the action of the rays of 

 light; The latter is mofl: probable. Wc havefeen a variety 

 of methods by which heat is produced. They appear in 

 different forms, but they all terminate in the fame thing; 

 they are difl'erent methods of exciting a tremulous motion 

 in the particles of the body. By feme of them the mofl: 

 intenfe heat is produced, and yet in no cafe is there any 



adual addition of fire. When heat is excited by the Sun, 

 there is alfo a tremulous motion excited in the particles of 

 the body, they are expanded, q^c. The phenomena re- 

 femble thofe of heat excited by other means, whence it 

 feems unphilofophic to fuppofe that there fliiould be an ac- 

 ceflion of fire in this cafe more than in the others. I there- 



njuhich is caitft 



of the 



of 



dijlance ft 



of 



thefe 



the Jitnefs of 

 vibrations zv 



K _, 



it is that the air which is very elafl:ic, when well com- 

 prefTcd by the weight of the incumbent atmofphere, will 

 receive a great degree of heat near the luriace of the 

 earth, while the light thin air whofc particles are removed 



Vol. I. 



T 



to 



