Acoustics & Sound For Musicians - Online Book

The Theory Of Sound Which Constitutes The Physical Basis Of The Art Of Music.

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	42                           MARIOTTE'S LAW                    [I. § 20. air, is not permanently affected by the motion of the piston. In order to retain the piston in its forward position, it is necessary to exert a force upon it in
	the direction of the arrow. If this force be relaxed, the piston will be driven back. Since the pressure of the air on the left of the piston is just what it was before, that on its right must necessarily have in­creased. But this increase of pressure is accom­panied by an increase of density due to the com­pression of the air on the right of the piston. Hence increase of pressure accompanies increase of density. If, as in (2), we reverse the process by moving the piston outwards, the extraneous force must be ex­erted in the opposite direction shown by the arrow. The pressure on the right of the piston is therefore less than the normal atmospheric pressure on its left,