rarefaction

He spoke in honeymoon whispers; but the rarefaction of the air was such that every word was audible.

This condition of a greater separation of the turns of the spring than usual is called a rarefaction.

A complete wave consisting of a condensation and a rarefaction is represented by that portion of the curve A-C.

So that if in this condensation any one affirmeth there is also some rarefaction, experience may assert it.

The rarefaction of the air and the rays of tile sun increased the dilatation of the gas; the balloon continued to ascend!