Analyfts of the Air. i6^ 
which I made by means of thefe inftru- 
ments, which I have here at firft deferibed, 
to avoid the frequent repetition of a deferip- 
tion of 'em. It is confonant to the right 
method of philofophifing, firft, to analizc 
the fubjeft, whofe nature and properties we 
intend to make any refearches into, by a 
regular and numerous feriesof Experiments : 
And then by laying the event of thofe Ex- 
periments before us in one view, thereby to 
fee what light their united and concurring 
evidence will give us. How rational this 
method is, the fcquel of thefe Experiments 
will (hew. 
The illuftrious Sir Ifaac Newton ( query 
3ift of his Opticks) obferves, that “ true 
permanent Air arifes by fermentation or 
heat, from thofe bodies which the chy- 
mifts call fixed, whofe particles adhere by 
a ftrong attraftion, and are not therefore 
feparated and rarified without fermenta- 
tion. Thofe particles receding from one 
another with the greateft repulfive force, 
and being mod difficultly brought toge- 
ther, which upon contad were moft ftrong- 
ly united. And query 30. denfc bodies by 
fernaentation ratify into feveral forts of 
M 3 “ Air, 
