Heat, as the principle of expansion, rarefies and volatilizes all bodies; and then, as the heavier give place to the lighter, so bodies subject to its action ascend, and carry up with them the principle, matter, or action of heat.
"A Morning's Walk from London to Kew"
Richard Phillips
108. It is impossible that the spirit, incorporated with a certain quantity of air, should move this air; and this is proved by the passage where it is said that "the spirit rarefies that portion of the air with which it is mingled."
"Thoughts on Art and Life"
Leonardo da Vinci