CHAP. VII.

THough the Experiments deli∣vered in the foregoing Chap∣ter have, I presume, sufficiently ma∣nifested, that the modification given to the motions of the Air by sono∣rous bodies may have considerable effects upon Animals, in whose or∣ganized bodies the curiously contri∣ved parts have an admirable con∣nexion with, and relation to, one another, and to the whole Symmetri∣cal fabrick they make up; yet, I fear, it will scarce seem credible, that sonorous motions of the Air, not very loud, should find, even in Page  80 bodies Inanimate and Inorganicall, such congruous Textures and other Dispositions to admit their action, that even more languid Sounds, pe∣culiarly modified, may sensibly ope∣rate upon them, and much more than sounds that are louder and more ve∣hement, but not so happily modified. To make this good by particular Ex∣periments, I shall begin with that, which, though the effect may seem inferiour to that of most of the o∣thers, I judge fittest to manifest, that the produced motion depends upon the determinate modification of that of the impellent Fluid.

That a certain impulse of Air, made by one of the Unison-strings of a Musical Instrument, may suffice to produce a visible motion in ano∣ther, is now become a known expe∣riment; of the Cause and some un∣observed Phaenomena of which I else∣where more fully discourse. But, that it may not be suspected in this case, that the shake of the untouched string is communicated to it by the Page  81 propagated motion of the Instrument it self, to which the string, that is struck, is also fastned; I shall add, that, according to what I elsewhere re∣late, I found by trial purposely made, that a string of Wire, (which you will grant to be a more solid body than an ordinary Gut-string,) may be without another string brought to tremble by a determinate Sound made at a distance, which produced but such an impulse of the Air, as could neither be seen nor felt by the By-standers, nor would communicate any sensible motion to the neigh∣bouring strings. 'Tis true, that in this case the string, in which the trem∣bling was produced, was a single, long, slender and springy body, fast∣ned at both ends to a stable one; and therefore it may seem altoge∣ther groundless to expect, that any thing like this effect should be by the same cause produced in bodies that do not appear so qualified. But, as we elsewhere shew, that a certain degree or measure of tension is in or∣der Page  82 to this Phaenomenon the principal Qualification, without which all the other would be unavailable; perhaps 'twill not be absurd to enquire, whether, in bodies of a very differing appearance from strings, the various Textures, Connexions, and Compli∣cations, that Nature or Art, or both, may make of the parts, may not bring them to a state equivalent to the Tensions of the strings of Musical Instruments, whereby divers of the mentioned parts may be stretched in the manner requisite to dispose them to receive a vibrating motion from some peculiar Sounds: And whether these trembling parts may not be nu∣merous enough to affect their neigh∣bours, and make, in the body they belong to, a tremulous motion dis∣cernible, though not by the Eye, yet by some other sense. This conjecture or inquiry you will, I hope, have the less unfavourable thoughts of, when you shall have considered the following Experiments.

I remember, that many years agoe Page  83 I found by trial, that, if a somewhat large and almost hemispherical Glasse, though not very thin, were conve∣niently placed, a determinate sound, made at a convenient distance from the concave surface of the Glasse, would make it sensibly ring, as a Bell does a while after it has been struck. But this noise was the effect of a de∣terminate sound; for, though the voice were raised to a higher tone, or if the sound were made louder, the same effect would not insue. I remember also, th••, some years after, I observed, that large empty drinking∣glasses of fine white metal had each of them its determinate Tension, or some disposition that was equivalent as to our purpose. For, causing the strings of a Musical Instrument to be variously screwed up, and let down, and briskly struck, we found, as I expected, that the motion of one string, when 'twas stretched to a certain note or tone, would make one of the Glasses ring, and not the other; nor would the sound of the Page  84 same string, tuned to another note, sensibly affect the first Glasse, though perhaps it might have its operation upon another. And this Circum∣stance is not, on this occasion, to be omitted, that, after we had found the tone proper to one of the Glasses, and so tuned the string, that, (I say) when that was struck, the Glasse would resound. Having afterwards broken off a part of the foot of the glass, yet not so much but that it con∣tinued to stand upright, the same sound of the string would no longer be answered by the Vessel, but we were obliged to alter the tension of the string, to produce the former ef∣fect. The Learned Kircherus, as I have been informed, somewhere mentions a correspondence between some li∣quours and some determinate sounds; which I suppose may be true, though the triall did not succeed with me, perhaps for want of such accommo∣dations for so nice an Experiment as I could have wished, but could not procure: But if you can, you will ob∣lige Page  85 me to make the trials so as to sa∣tisfie your self and me, whether the agitation of the liquour be caused im∣mediately by the motion of the Air, or be communicated by the interven∣tion of the tremblings of the Vessel.

An Artist famous for his skill in making Organs, answered me, that, at some stops of the Organs, some seats in the Church would tremble. But, because I suspected by his Re∣lation, that the greatness of the sound chiefly effected it, because, when that Pipe, which they call the open Diapason, sounds, the chair or seat, on which the Organist sits, and per∣haps the neighbouring part of the Organ trembles; I shall add, that I have divers times observed certain sounds of an excellent Organ to make not onely the seat, I sate on in the Church, tremble under me, but pro∣duce an odd tremulous motion in the upper part of my Hat, that I could plainly feel with my hands. And that, which makes me apt to believe that this effect depends upon the de∣terminate Page  86 tone, rather than upon the loudness of the sound, is, that I have oftentimes felt, and diligently obser∣ved such a kind of motion in the up∣per part of my Hat, upon the pro∣nouncing of some words in ordinary discourse; in which case the effect could not with probability be refer∣red to the greatness of the Sound, but its peculiar fitness to communicate such a motion to a body so disposed.

Nor is it onely in such small and yielding bodies, as Hats and Strings, that Sounds that are not boisterous may produce sensible effects, for, if they be congruous to the Texture of the body they are to work on, they may excite motions in it, though it be either solid or very bulky: of which I shall here subjoyn a couple of instances.

An ancient Musician affirmed to me, that, playing on a Base-viol in the chamber of one of his Scholars, when he came to strike a certain Note on a particular string, he heard an odd kind of jarring Noise, which he Page  87 thought at first had either been casu∣al, or proceeded from some fault in the string; but, having afterwards frequent occasion to play in that same room, he plainly found, that the Noise, he marvelled at, was made by the tremulous motion of a Casement of a window, which would be made to tremble by a determinate sound of a particular string, and not by o∣ther Notes, whether higher or lower.

To this first Instance I shall add the second, which, I confesse, I was not forward to believe, till trial had con∣vinced me of the Truth; and I scru∣pled it the rather, because, if the re∣flexion of determinate Sounds should appear to proceed from the peculiar kind of tremulous motion into which the parts of the resonant body are put, it may incline men to so great a Paradox, as to think, that such a motion of the Air as our Bodies do not feel, may produce a trembling in so solid a body as a Stone-wall of a great thickness. The Experiment or Observation it self I shall give you Page  88 in the same words I set it down some hours after I made it, which were these.

Yesterday I went to satisfy my self of the truth of what had been told me by an ancient Musician, to whom I had been relating what I had observed of the effects of some de∣terminate Sounds even upon Solid bodies, and of whom I enquired, if he had met with any thing of the like nature: taking him along with me, I found, that though the place be but an Arch, yet it would not answer to all notes indifferently, when we stood in a certain place, but to a determi∣nate Note, (which he afterwards told me was Ce fa ut a little flatted,) to which note it answered very reso∣nantly, and not sensibly to others, which we made trial of, whether higher or lower than it; and, (which added to the strangeness,) when I made him raise his voice to an Eighth, as consonant as those two Sounds are wont to be in all other cases, the vaulted Arch did not ap∣pear Page  89 to us affected with the Note. The Musician added, that he had tried in most Arches all about the City, and could not find such a pe∣culiarity in them, as being to be made resonant by all Notes or Sounds indifferently that were strong e∣nough; and also, that as this Arch for this hundred years has been ob∣served to have this property, so an ancient and experienced Builder in∣formed him, that any Vault that were exquisitely built, would peculiarly answer to some determinate Note or other.