[ xxii ] 



quiries for the moll part imitated, I 

 cannot but think more favourably 

 of the importance of this difcovery 

 than the author himfelf does. I 

 even think with the Abbe, that, by 

 tiling convenient and accurate in- 

 ftruments, and by obferving to the 

 greater! nicety all the manoeuvres of 

 the operation conftantly in the fame 

 Way 3 we may with as much preci- 

 lion judge of the degree of purity 

 of common air, as we now are able 

 to judge of its degree of heat and 

 cold by a good thermometer. 



Indeed, by this method, even all 

 the changes which the constitution, 

 of the atmofphere undergoes daily, 

 in the fame place, are obferved with 

 fo much accuracy, that, by making 

 ten obfervations with the fame air, 

 the difference will fcarcely amount 



to. 



