252 On the Proportion of 



air with 60 hydrogen, become 100 after the 

 explosion, and no oxygen is found in the re- 

 siduum ; here 21 oxygen take 39 hydrogen. 



2. Of the weight of the Aqueous Vapour 

 Atmosphere, 



I have, in a former essay, (Manchester 

 Mem. vol. 5. p. 2, page 559.) given a table of 

 the force of vapour in vacuo for every degree 

 of temperature, determined by experiment ; 

 and in the sequel of the essay, have shewn that 

 the force of vapour in the atmosphere is the 

 very same as in vacuo, when they are both at 

 their utmost for any given temperature. To 

 find the force of aqueous vapour in the at- 

 mosphere, therefore, we have nothing more 

 to do than to find that degree of cold at which 

 it begins to be condensed, and opposite to it 

 iri the table abovementioned, will be found the 

 force of vapour. From the various facts men- 

 tioned in the essay it is obvious, that vapour 

 contracts no chemical union with any of the 

 gases in the atmosphere ; this fact has since 

 been enforced in the Annales de Chimie, 

 vol. xlii. by Clement and Desorme. 



M. De Saussure found by an excellent ex- 

 periment, that dry air of 64*^ will admit so 

 much vapour as to increase its elasticity, -^V . — ■ 



