a stream of air driven through a pipe with a lateral aperture, like a French flute. where at the part where the stream issues out of the orifice, vibrations are manifestly perceived, which are rendered still more evident if the current be impregnated with smoke.
4. Of the Velocity quound.-—The velocity of any impression transmitted by the common air, being corrected by the experiments of various observers, is at an average here estimated at 1130 feet in a second of time.
5. Of Sonorous Cavities.—,—What is here said relates chiefly to the reflection of sounds in rooms or galleries. This we find takes place as often in a second as double the breadth of the room or passage is contained in 1130 feet, that breadth determining the pitch of the musical note thereby produced.
6 Of the Divergence of Sounds—Various observations are here related which militate against the received opinion that sound diverges equally in all directions, and that there is no substance impervious to sound. On this head, however, the author admits that a more ample investigation will be required than has hitherto been instituted; and he intimates that he shall engage in it as soon as his leisure will permit.
7. 0f the Decay of Sonnet—The two hypotheses, lst, that sound decays nearly in the simple ratio of the distances, and 2nd, that this diminution is in the subduplicate ratio, are here stated, and some fallacies are mentioned, which will likewise render a further inquiry necessary.
8. Of the Harmonic Sounds of Pipes.-—The object of this section appears from a table exhibiting the results of a set of experiments, made with a view to ascertain the velocity with which organ-pipes of different lengths require to be supplied with air, according to the various appropriate sounds which they produce.
These were made on pipes of the same bore, and of different lengths, both stopped and open. The general result was, that a similar blast produced as nearly the same sound as the length of the pipe would permit, or at least that the exceptions, though very numerous, lie equally on each side of this conclusion.
9. Of the Vibrations of different Elastic Fluids.—The difference of these vibrations has been received as being reciprocally in the sub-duplicate ratio of the density of the fluid. Hence in pure hydrogen gas they must be 3'6 times greater than in common air. And this will explain why an instrument will often appear out of tune, when, in fact, the fault lies in the change of temperature of the atmosphere; and why the pitch of an organ will be found to differ materially in summer and winter.
10. Of the Analogy between Light and Sound.—While the author vindicates the Newtonian theory of light against the criticisms at Euler, he freely admits that it is liable to some objections upon which he chiefly insists upon the uniformity of the motion of light the same medium, and the partial reflection from every refracting surface. Having reasoned largely upon this subject, he admits the
