228 OF SOUND AND HEARING. 



air than of itself. Also in eruptions, there is percussion 

 made of the spirit breaking out against the air adjacent; 

 as in the cracklings made by dry leaves, or bay salt, and 

 many other things, when cast into the fire; and in thunder, 

 either by the spirit breaking out from the cloud, or wal 

 lowing and tossed to and fro, as in the more hollow and 

 lengthened rolling of thunder; also we see in sport that a 

 fresh rose leaf gathered together so as it shall contain air, 

 and struck upon the back of the hand or upon the forehead, 

 cracks by eruption of the air. 



Instances of the percussion of an hard body against the 

 air are seen in musical stringed instruments; in the whist 

 ling of an arrow, as it flies through the air; in the beating 

 of the air, although it strike not any hard body; also, in 

 regals their sound is given by the air striking against water, 

 in the pipe they call the nightingale-pipe, which gives a 

 sound continually tumbling; in water agitated and restoring 

 itself again ; and in the toys wherewith children please 

 themselves (they call them cocks) in imitating of the voices 

 of birds, likewise in other hydraulics. 



Instances of the percussion of an hard body against an 

 hard body are found either simply, or with communication 

 of some air inclosed beside that air, which is cut or elided 

 between the hard bodies percussed ; simply, as in all ham 

 mering or knocking of hard bodies, with communication of 

 air penned in, as in bells and drums, 



A stone cast forcibly into the water gives a sound ; as 

 do the drops of rain falling upon the water, and no less 

 wave dashing against wave, in which there is percussion 

 betwixt an hard body and water. 



It seemeth to be constant in the generation of all sound, 

 that there are certain parts of air, and that air is required 

 between the bodies percussed ; which air, in the percussion 

 of an hard body against the air, and of an hard body 

 against an hard body, appears manifestly to be cut or 

 elided. I judge that flame should suffice for this in the 

 stead of air, as if in the midst of a great flame a bell should 

 be rung, or stones knocked together ; but in the percussion 

 of air against air this elision or separation appears more 

 dark, but the air seems only to be beaten and driven, and 

 that in a soft voice, very gently. But it seems, even in 

 this kind, to need that there be some elision of the air 

 percussed by the air percussing : for even in air moved by 

 a fan, the air from the side of the fan, and when air is 

 blown out of bellows, the blast of air from the mouth, 



