of Strings and Rotht 11^ 



t*ie firft toiie of the fame rod when perfeflly free. All kinds 

 of longitudinal vibrations can be beft produced by proper 

 friftion or nibbing in the direftion of the length with the 

 finger, or any foft fubftance rubbed over with pounded refm, 

 and on glafs rods, of which thofe ufed for tliermometers and 

 barometers are the fitteft, with a wet ragbeftrewed with fine 

 fand; from which it k evident that the rubbing muft be per- 

 formed within a vibrating part, and that the rod muft be 

 gently held between two fingers of the other hand at any of 

 the refi;ing points, but at no other place. In pipes the higher 

 tones are produced by a ftronger and fomewhat different me- 

 thod of blowing. In a pipe open at both ends, the column 

 of air contained in it vibrates like a rod free at both ends; 

 and the column in a pipe clofe at one end, like a rod which 

 is fixed at one end. In all longitudinal vibrations, the toncs^ 

 during the fame kind of vibration, depend merely on the 

 length of the fonorous body, and on the quality of the fub- 

 ftance : the ihickncfs, and other circumftances in regard to 

 form, are of no confideration. I have examined every fub- 

 ftance which I could obtain in a fufficiently long rod-like 

 form, in regard to longitudinal vibration ; for example, many 

 kinds of wood and metal, alfo glafs, w halebonc, &c. The 

 fpccific gravity makes no difference ; for fir-wood, glafs, and 

 iron, give almoft the fame tone, as alfo brafs, oak, and the 

 flianks of tobacco-pipes made of clay. 



As found is conduced alfo by longitudinal vibrations, fince 

 a portion of air, or of any other fubftance, is obliged by the 

 impulfe of the fonorous body to contract and again expand 

 itfelf, a more accurate knowledge of longitudinal vibration 

 may ferve to determine with what velocity found is condu6led 

 through hard bodies. Count Giordano Riccati, in his ex- 

 cellent work on Strings or ElalHc Fibres*, has proved that 

 found paflTes through a fpace filled with air, of a gi\'en length, 



• D( lie Conic ovvfro Fibre F.lafllche. Bologna, 1764. 4. S^lied. v, 

 $ 3. and Sciied. viii. dill. t. 



I i in 



