LITMIR.BIZ

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being an elastic Fluid, these Undulations are more quick and brisk in their Motions than in Water. So much for Sound itself. Now for the Cause of this Sound, or of these Undulations.

      These Undulations are caused by the Vibration of some elastic Body, which is put into Motion by a Stroke of another Body against it. It must be an elastic Body (take notice) for upon that Word depends the Truth of what is going to be alledged. To convince the Reader of the Truth of this, he has nothing to do but to take a Rolling Pin, and strike it against a Pound of Butter, and he will find very little or no Sound at all, because Butter has very little Elasticity or Spring in it; but if he strikes the aforesaid Implement against the Table, he will find Sound enough, because most Tables are made of Wood, which is a very elastic Body. If there is no Butter in the House, Wax will do as well or better, for it will prove that a Body may be hard without being elastic, and which will be very much to the Purpose. It will be necessary, before we can get any further, to explain what Vibration is, a Word very commonly made Use of among Musical Men, tho' but little understood.

      To be as short as possible; a Piece of Lead hung upon the End of a String, which moves backwards and forwards of itself after being first put into Motion, is called a Pendulum, and that Motion backwards and forwards is called its Vibration; it is upon this Principle that elastic Bodies are the Cause of Sound. It will be best illustrated in a Musical Instrument, besides that is the Point in Hand; and to be more to the Point still, we will suppose it a Violin, though any other stringed Instrument would answer the same End.

      Here we have four Strings stretched out upon a Bridge, or thin Piece of Wood, which communicates to the Belly of the Instrument, from which Belly the greatest Part of the Tone proceeds. Now a String drawn tight at both Ends, when it is struck, will have a Vibration or tremulous Motion, which Vibration, or tremulous Motion, acts upon the same Principle as a Pendulum does in a Cycloid, or, to speak as plain as possible, as a Pendulum does when it is put into it's proper Motion.

      It is upon this Principle of Vibration then, or tremulous Motion, that the String of a Violin, being moved by the Bow, is to act: The String immediately communicates it's tremulous Motion to the Bridge, and the Bridge to the Belly of the Instrument, which Belly being made of a very elastic Wood, by it's Vibration and free Motion, acts upon the Air in the Manner abovementioned.

      As it is the great Elasticity of the Wood which is to cause the Tone, it ought to have as little Confinement in it's Vibrations as is possible; the Weight of the Strings must indeed press against it, otherwise they could not communicate their Motion to it. We should therefore be careful not to over-string the Instrument, since it so plainly contradicts the Principles of Pneumatics.

      It is easy to hear when an Instrument is over-strung; and sometimes an Octave in a Harpsichord, by it's additional Number of Strings, shall render the Tone of the Instrument so dead, that, though it gives a Sprightliness peculiar to an Octave, yet it sometimes hardly compensates for the Loss of Tone which it causes in the Unisons, by it's too great Pressure upon the Belly of the Instrument.

      And yet notwithstanding all this, what is more common than to see a Performer, with his Waistcoat unbuttoned, laying Strokes on a Violin, heavy enough to fell an Ox.

      The Truth is, managing the Bow is slight, and we must make Use of Art more than Strength in our Performance: moreover, it is an Art which cannot be wrote down upon Paper, nor explained in Words, but must be learned by the Example and Direction of some assiduous Master. However what has been said may serve to shew, from Philosophical Principles, the Error of leaning too hard upon the Instrument, which was the Thing intended to be done.

      V

      That the farther you go South, the hotter is the Climate.

      Gentle Reader, as thou art a Person of Understanding, thou wilt pardon the Want of Connection and Form which thou findest in the different Subjects which are here started for thy Entertainment: It would be very easy, in the fair Copy which will be wrote over, to range them, in an Order, suitable to the different Branches to which they belong; but why should I pester thee with Form, when there is nothing so agreeable to a Man of Taste as an easy Variety? Therefore, though it is ten to one that, before I have done with thee, I shall have some more Discourse with thee about Musical Instruments, yet I shall not humour thee as a Critic so much as to give thee it now; well knowing, that if thou art determined to Review me, thou mayest find Abundance of other Opportunities for it in this Book: And likewise, that if thou dost approve of what is here discussed, thou wilt, if thou art a good-natured honest Fellow, pass by a little Incorrectness; for what else can a Man hope for in a Book which treats of nothing but Blunders? However the two following Sections may afford thee some Entertainment, if thou art a Man of Learning, and if thou art not a Man of Learning, they will give thee some Instruction; and to tell thee the Truth, the Subject of them is so Philosophical, that if we were not fully convinced of the Truth of what will be alledged, we should be afraid to undertake it.

      For in this little Pamphlet, Philosophy will be avoided as much as possible, that is, it never will be introduced at all, unless it is absolutely necessary to call in it's Aid, in order to prove the Truth of any Thing which shall be asserted. But to the Point; which is, to rectify the vulgar Error, which supposes, that the farther a Person goes South, the hotter will be the Climate.

      This is so well known to be an Error, by all Men of Science, and by all Navigators, that it is needless to say much about it, only just to relate the Truth, that those who are mistaken in their Way may be set in the right Road. But to proceed.

      The two Poles of the Earth, that is, the two North and South Extremities of the Globe, are in such a Position, or are so inclined to the Sun, or to the Plain of the Ecliptic, as never to have any Rays fall directly over their Heads, or they never have him any higher than a little above their Horizon, or the Surface of the Earth; for which Reason it is always cold at the North and South Poles, which will naturally be the Case, as any one may experience by the different Position of the Sun, in Summer and Winter, in our own Climates.

      The Case is exactly contrary at the Æquator, or on the Middle of the Globe, which is farthest from the two Poles, for there they have the Sun over their Heads at Noon all the Year round; for which Reason it is always hot under the Line, yet not always the hottest of any Part of the Globe, as has been sometimes philosophically supposed, and which shall be the Subject of the next Chapter, to introduce which this was principally intended.

      VI

      That exactly under the Æquator is always the hottest Climate on the Globe.

      This Error by no Means ought to be called a vulgar one; because it is a Course of Philosophical Study, joined to a Want of Experience, which gives Occasion to it. It is the Result of a Knowledge of the general Cause of Heat and Cold, in different Degrees of Latitude upon the Surface of the Earth; which Knowledge is apt to apply the Rules of Astronomy, that explain the Phœnomena of Nature in general, to every Purpose that offers itself, in all Cases, without being able to search into the individual Parts of a System, on Account of the Distance of the Objects which are the Subjects of Enquiry. For though, as has been said before, for a just Astronomical Reason, the Position will hold good, that those Inhabitants who are under the Line, live in the hottest Climate in general, yet it is proved by the Experience of Navigators, that in several Parts under the Æquator there is a fine, mild, soft Climate, even excelling any of those in the temperate Zones; so happily are Things disposed for the Purposes of Animal Life, by the Author of Nature.

      This is a Truth which we are constrained to believe, as we have so many living Witnesses in our own Country, who are ready to assert it.

      We have one accurate Account in Anson's Voyage, where the Author reasons very Philosophically upon the Subject. This Author tells us, that the Crew of the Centurion were in some Uneasiness about the Heat of the Climate, which they expected they were to undergo, when they came to that Part of the Æquator which is near the American Coast, upon the South Sea; but that when they came under the Line, instead of those scalding Winds which sometimes blow in immensely hot Climates, they were agreeably surprized with the softest Zephyrs imaginable; and that, instead of being scorched by the perpendicular Rays of the Sun, they had a fine Covering of thin grey Clouds over their Heads, and just enough of them to serve for a Screen, without looking dark and disagreeable. Many other Beauties

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