The works of the Honourable Robert Boyle, Esq., epitomiz'd by Richard Boulton ... ; illustrated with copper plates.

EXPERIMENT XXVII.

IT hath been the receiv'd Opinion of the Schools, That the Air is the Medium, through which Sounds are conveigh'd: But the Indu∣strious Kircher having observ'd, that if a Bell be fix'd in the upper end of a Tube, and, upon making the Experiment de Vacuo, be left there, a Load-stone apply'd to the side of the Tube, will attract the Steel-clapper; which, upon a Re∣moval of that Load-stone, will fall upon the other side of the Bell, and cause an Audible Sound: He thence infers, That the Medium through which Sounds are conveigh'd, must be much more subtle than the Air. But to evince the contrary, we suspended a Watch in our Receiver, by a Packthred, and observ'd, That the Sound was not only audible at the sides of the Receiver; but that that which was likewise perceiv'd by the Ear, held near the Cover, was different from that which we heard at the sides of the Receiver; but the

Air being drawn out, we could not perceive the least Sound, tho' the Motion of the Minutes assur'd us, that the Pendulum continu'd it's Mo∣tion; yet upon admitting of Air again into the Receiver, the Sound was again renew'd; which Experiment seems to evince, that the Air is the Chief Medium, through which Sounds are con∣veigh'd: Yet it is not a little strange, that so slight a Stroke as that of the Pendulum, should give such an Impulse to the Ambient Air, as to inable it to communicate a Motion to the sides of the Receiver, strong enough to put the External Air into an Undulating Motion.

But having supported a Bell in the Middle of our Receiver, by a large Stick, which reach'd from one side to the other, the Diameter of the Bell, being about two Inches, we observ'd, that tho' the Sound in the Receiver, was not equally as sharp as in the open Air; yet there was no considerable Variation, when the Air was drawn out; which evinces, that a subtler Medium than the Air, is not altogether incapable of propa∣gating Sounds, no more than Air; however, in the foregoing Experiment try'd with a Bell, su∣spended in a Glass-Tube, it may not without Reason be suspected, that the Cavity of the Tube was not wholly void of Air, since Expe∣rience informs us, that it is impossible to fill the Glass-Cylinder, so as to keep the Upper Part of the Tube void of Air, since the Aery Parts lodg'd in the Pores of the Mercury, fly up into it.

And further on this Occasion, to shew how far the Air is the Principal Medium of Sounds, we might alledge, that it was observable in a

former Experiment, that tho' upon the strik∣ing of Fire, with the Lock of a Pistol in our Receiver, the Sound is audible; yet it is much more dead, than when made in the open Air: And the like Variation is observable in all other Sounds made in our Receiver.

Notes

• Concerning the Propa∣gation of Sounds.