[ i8o ] 



this head is fo much the greater 

 when dephlogifticated air is under 

 examination. 



I have now pointed out twenty 

 fources of errors, which may be 

 committed in the examination of 

 the falubrity of different airs, which 

 indeed it would be impofTIble to 

 commit all in one and the fame 

 trials, but of which fome are con- 

 tinually committed in the methods 

 hitherto in ufe, and which render 

 the accuracy of the teft as uncertain 

 as the experiment itfelf is : how- 

 ever, I readily acknowledge, that 

 even an accurate philofopher, pro- 

 vided with the fame initruments 

 which the Abbe ufes, will find it 

 difficult in the beginning to make 

 two experiments with fuch nicety 

 as not to obtain a difference of fome 

 few fubdivifions ; but he will by a 



little 



