Translation of Key's Essays. 61 



Essay XIV. 

 Fire can thicken Air. 



The reasons discussed in the 11th Essay, are sufficient to 

 satisfy an unprejudiced mind that fire heating air subtilizes and 

 separates some of its parts, and that this separation is neces- 

 sarily followed by the thickening and increase of weight of the 

 others. But since this truth is obstinately contested, in order 

 to exhibit it more clearly, I demand that a laboratory be pre- 

 pared for me in the region of elementary fire, adjoining that of 

 air, and in it I will shew them ocularly what they are unwilling 

 to believe. For as the vessels which we here call empty are 

 nevertheless full of air, so will they be there full of fire. And 

 since when we pour v/ater into an alembic, the previously- 

 enclosed air is expelled, so will fire give place to the air which 

 in that region shall be poured into the alembic ; and when put 

 upon the furnace will distil over drop by drop into the receiver, 

 and the first measure of it that is collected will be more subtle 

 than the second, the second than the third, and so on to the end. 

 What is more, the difference in subtlety and weight between the 

 first and last measure will be as perceptible as in those of dis- 

 tilled water. Now if any one laugh at my demand, let him know 

 that the great Archimedes required, in a like case, that a spot 

 should be given him in the region of air where to place his 

 engine, and he then promised to lift up the whole earth. (Ao; 9ra 

 ffxto, Kcci Tr,v ynv xmncru,) Not that he supposed that what he 

 demanded could be done, (for in the estimation of the wisest 

 men he was neither madman nor fool,) but he made it, confident 

 in the certainty of his demonstrations, and for clearer evidence 

 of the truth of his assertions. My demand too has no other 

 object. Whoever would see a thing approaching to this, with- 

 out having recourse to an impossibility, let him place an alembic 

 of extraordinary dimensions on a furnace, and having fixed a blad- 

 der, emptied of its air, to the highest part of the head by a small 

 pipe, begin to heat it ; the air of the alembic will then begin to di- 

 lute, and being no longer retainable in its original space, will rush 



