I 346_] 



"But I ftrongly fufped that the original experiment, on which 

 this calculation is founded, is erroneous, chiefly by reafon of the 

 flrong adherence of moifture to cold glafs, as will hereafter be 

 feen in treating of dew. From Schmidt's experiments, it may 

 be inferred, that the fpecific gravity of vapour diffolved in air at 

 this temperature is much lower with refped to that of pure air 

 than Sauffure has ftated, for he tells us that about 1066 meafures of 

 dry air in temperature 65'' would, if faturated with moiflure at that 

 temperature, occupy the fpace of about rico meafures, and confe- 

 quently receive an augmentation amounting to about y^ of their 

 bulk; now, transferring this ratio to the cubic foot in SaufTure's 

 experiment, it appears that — of a cubic foot thus added to the 

 cubic foot of dry air v/eighs 10 grains; but a cubic foot of dry 

 air, augmented by an acceffion of y- of fimikr air, would weigh 

 751 -|- 23,46 grains, which approaches nearly to Mr. Watt's ratio, 

 therefore the fpecific gravity of vapour diffolved in air at this 

 temperature is to that of perfedly dry air as 10 to 23,5 nearly. 

 It fhould however be recolleded that Mr. Sauffure found that a 

 cubic foot of dry air in reality took up 11,069 grains of moifture 

 when faturated at this temperature, and that it was only by way 

 of conceffion to thofe againft whom he argued, that he ftated the 

 weight taken up at 10 grains; then we fliould have of 11,069 to 

 21,195, or in round numbers as 11 to 21 or 10 to 19. And it 

 fliould -farther be remarked, that the temperature is given very 



loofelv. 



•'-1 



