Ii6 On the longitudinal Vihrations 



in the fame time that a column of air of the fame lengtli^ 

 contained in a pipe open at both ends, makes one vibration. 

 Newton in his Prz«c//)ifl * fays the fame thing in another 

 manner, for he aflerts that each ftroke (pulfusj paflTes through 

 twice the length of an open pipe; but he calls a double 

 vibration, that is, a contra6lion and expanfion, a ftroke ; 

 whereas Riccati and others, agreeably to the common mode 

 of expreffion, call each contraftion, as well as each expanfion, 

 a vibration. The principles on which this propofition de- 

 pends, feem to be of fuch a general nature that they may be 

 applied to hard bodies; and thus we may at leaft admit, with 

 the greateft probability, that found pafles through everybody 

 in the fame time in which that body, when it vibrates freely, 

 makes one longitudinal vibration. We are taught by expe- 

 rience, that found moves through the air with a velocity of 

 about 1040 Paris feet in a fecond; we learn alfo from expe- 

 riments and calculation, that in a fliut pipe of five feet, and 

 an open pipe of ten feet, 100 vibrations are made in a fecond. 

 According, then, to the above propofition,. found muft pafs 

 through ten times a hundred, that is, 1000 feet in a feeond. 

 That the velocity is fomewhat greater, being about 1040 feet, 

 does not however contradift the propofition ; for the column 

 of air aftually agitated by the founding of a pipe, is always 

 a little longer than that contained in the pipe ; as Count Ric- 

 cati has proved in the before-mentioned work, and as peopk 

 may be eafily convinced through experience, by holding the 

 hand clofe to the mouth of a pipe, where the vibration of the 

 air will be ftrongly felt. Hard bodies, if the above propofi- 

 tion be univerfally true, muft conduft found with greater ve- 

 locity in proportion as the tone is higher, which is emitted 

 by the fame length and with the fame kind of longitudinal 

 vibration. Now the tones of a rod of tin are about two oc- 

 , laves and a large feventh higher; one of filvcr, three oclavcs 

 and a whole tone ; one of copper, nearly three o<5lavcs and a 



* Pilnc, Philof. Nat. lib. ii. prop. 50. in fchol. 



fifth J 



