124 Dr. Young's Experiments and Inquiries. 



IX. Of the Vibrations of different elastic Fluids. 



All the methods of finding the velocity of sound, agree in 

 determining it to be, in fluids of a given elasticity, reciprocally 

 in the subduplicate ratio of the density : hence, in pure hydro- 

 gen gas it should be 1/13 = 3.6 times as great as in common 

 air; and the pitch of a pipe should be a minor fourteenth higher 

 in this fluid than in the common air. It is therefore probable that 

 the hydrogen gas used in Professor Chladni's late experiments, 

 was not quite pure. It must be observed, that in an accurate 

 experiment of this nature, the pressure causing the blast ought 

 to be carefully ascertained. There can be no doubt but that, in 

 the observations of the French Academicians on the velocity 

 of sound, which appear to have been conducted with all possible 

 attention, the dampness and coldness of the night air must have 

 considerably increased its density : hence, the velocity was found 

 to be only 1109 feet in a second ; while Derham's experiments, 

 which have an equal appearance of accuracy, make it amount to 

 1 142. Perhaps the average may, as has been already mentioned, 

 be safely estimated at 1130. It may here be remarked, that the 

 well known elevation of the pitch of wind instruments, in the 

 course of playing, sometimes amounting to half a note, is not, 

 as is commonly supposed, owing to any expansion of the 

 instrument, for this should produce a contrary effect, but to 

 the increased warmth of the air in the tube. Dr. Smith has 

 made a similar observation, on the pitch of an organ in summer 

 and winter, which he found to differ more than twice as much 

 as tlie English and French experiments on the velocity of sound. 

 Bianconi found the velocity of sound, at Bologna, to differ at 

 different times, in the ratio of 152 to 157. 



