ON THE PROPAGATION OF SOUND. 291 



not appear to have been so great in any experiment hitherto made on the 

 soiftids of pipes in gases of different kinds. For such experiments, the 

 comparative specific gravity of the gas may be most conveniently ascer- 

 tained by Mr. Leslie's method of observing the time employed in emptying a 

 vessel through a small orifice, by means of the pressure of an equal column 

 of water ; according to the simple theory, the velocities of the gas thus 

 discharged ought to be in the same proportion as the respective velocities 

 with which sounds would be transmitted by them ; and if any variation 

 from this proportion were discovered, it must be attributed to the different 

 degrees of heat produced by condensation in the different fluids. Steam, 

 at the temperature of boiling water, is only one third as heavy as common 

 air ; consequently the velocity of sound in steam must be nearly three 

 fourths greater than in air. 



It does not* appear that any direct experiments have been made on the 

 velocity with which an impulse is transmitted through a liquid, although 

 it is well known that liquids are capable of conveying sound without diffi- 

 culty ; Professor Robison informs us, for example, that he heard the sound 

 of a bell transmitted by water at the distance of 1200 feet. It is, however, 

 easy to calculate the velocity with which sound must be propagated in any 

 liquid of which the compressibility has been measured. Mr. Canton has 

 ascertained that the elasticity of water is about 22,000 times as great as 

 that of air ; t it is, therefore, measured by the height of a column which is 

 in the same proportion to 34 feet, that is 750 thousand feet, and the velocity 

 corresponding to half this height is 4900 feet in a second. In mercury, 

 also, it appears from Mr. Canton's experiments, J that the velocity must be 

 nearly the same as in water, in spirit of wine a little smaller. These 

 experiments were made by filling the bulb of a thermometer with water, 

 and observing the effects of placing it in an exhausted receiver, and in con- 

 densed air ; taking care to avoid changes of temperature, and other sources 

 of error : the fluid rose in the tube when the pressure was removed, and 

 subsided when it was increased. A slight correction is, however, required, 

 on account of the expansion and contraction of the glass, which must have 

 tended to make the elasticity of the fluids appear somewhat greater than it 

 really was. 



It is also well known that solid bodies in general are good conductors of 

 sound : thus any agitation communicated to one end of a beam is readily 

 conveyed to the ear applied to the other end of it. The motion of a troop 



* Since the above was written, experiments have been made on the velocity of 

 sound in water, by M. Beudant, at Marseilles, and MM. Colladon and Sturm, (a) in 

 the Lake of Geneva. The care with which the latter series of experiments were con- 

 ducted, and the distance to which the sounds were transmitted, amounting to about 

 four leagues, entitles them to confidence. The sounds were made by bells rung 

 under the water on one side of the lake, which were heard on the other side by the 

 intervention of a tube, closed at one end and open at the other ; the closed end being 

 immersed in the water, so that a column of air transmitted the sound to the ear 

 above the water. By a great number of experiments, it appears that the velocity is 

 4708 feet per second, in water of the temperature 46'6 of Fahrenheit. 



*t 21,740, according to Canton, Ph. Tr. 1762, lii. 640; 1764, liv. 261. 



J Ibid. 



(a) Annales de Chimie, vol. xxxvi. Comptes Rendus, xiii. 439. 

 u2 



