Conjideratlons on Dr. Hut Ion s Theciy of Rain. 59 



It appears they did. It would however be readily granted, 

 I fuppnfej by each of thefe pbiloiophers, that hypothefes, 

 of whatfoever kind, ought not to be admitted into fcience 

 without the molt rigorous examination, and that doubt has 

 a right to keep the door iliut until ibme paflTport of the de- 

 mondrative kind is obtained cither from nature or experi- 

 ment. A geometrical reprcientation of what may he is not 

 a fufficicnt foundation whereon to afiert what is a law of na- 

 ture. Let us therefore exam.ine how far this theorv, which 

 does not appear to be fupported by any direft experiment, 

 v'ill bear the teft of the excellent and decifive ones whereon 

 the doftrine of capricities has been eliablilhed by Black, 

 Crawford, and Lavoifier. 



The author firft aifumes, as a law of nature, the pofition, 

 that the (olution of water in air increafes with the tempera- 

 ture (h'-at), but in an increafmg ratio. On this he grounds 

 a fec()nd, the fubdance of which is, that if two portions of 

 air, faturated with water and at differing temperatures, be 

 mixed, the mean proportion will not be ioluble at the mean 

 teni|)erature, and therefore a part will be precipitated. 



The fiPft pofition may be true, or it mav not ; perhaps no- 

 thing fliort of atonal experiment can fatisfa6torily afcertain 

 the actual curve of evaporation*. 



The fecond depends entirely on conditions which the doftor 

 has t.iken for granted in each of the three cafes of evapora- 

 tion dated by him, and which, on the received principles of 

 caloric, can belong to no one of them. Thefe conditions 

 withdrawn, the theory of rain, like its fubjcft, falls to the 

 ground, and the diagram proves as unfubftantial as the bow 

 with which the {bower is decorated. To make this appear, 

 it is only neceflary to produce the following praftical refults, 

 which apply equally, whether we regard caloric as matter or 

 motion. 



A homogeneous fubOance, or two fubfiances having equal 

 capacities for caloric, beinjr mixed in equal portions at un- 

 equal temperatures, the temperature of the mixture is found 

 to be in the arithmetical mean. 



But heterogeneous fubffances, and thofc in other refpefts 

 homogeneous, but differing in capacitv, being mixed in likfe 

 manner, give a temperature which either exceeds or falls 

 below the arithmetical mean, and approaches towards that 

 of the two fubltances which pofTeired the greater capacity. 



♦ Experiments decifive of this very qucftinn were iiKide ahoiit tliis time, 

 and ttic ici'ultj prtdntcd to the Literary and Philofophical Society of 

 Manchefter by John Dalton, efc}. VVc Ihall have occal'ion to notice his 

 paper further on. 



The 



