This is a very bold Aſſertion, but it may be true for ought we know, and the Inhabitants of the Planets may poſſibly have a greater inſight into the Theory of Muſick than has yet been diſcover’d among us. For if you ask any of our Muſicians, why two or more perfect Fifths cannot be uſed regularly in Compoſition; ſome ſay ’tis to avoid that Sweetneſs and Luſhiouſneſs which ariſes from the Repetition of this pleaſing Chord. Others ſay, this muſt be avoided for the ſake of that Variety of Chords that are requiſite to make a good Compoſition; and theſe Reaſons are brought by Cartes and others. But an Inhabitant of Jupiter or Venus will perhaps give you a better Reaſon for this, viz. becauſe when you paſs from one perfect Fifth to another, there is ſuch a Change made as immediately alters your Key, you are got into a new Key before the Ear is prepared for it, and the more perfect Chords you uſe of the ſame kind in Conſecution, by ſo much the more you offend the Ear by theſe abrupt Changes. Again, one of theſe Inhabitants perhaps can ſhow how it comes about, that in a Song of one or more Parts, the Key cannot be kept ſo well in the ſame agreeable Tenour, unleſs the intermediate Cloſes and Intervals be ſo temper’d, as to vary from their uſual Proportions, and thereby to bear a little this way or that, in order to regulate the Scale. And why this Temperature is beſt in the Syſtem of the Strings, when out of the Fifth the fourth Part of a Comma is uſually cut off; This ſame thing I have formerly ſhew’d at large. But for the regulating the Tone of the Voice (as I before hinted) that may admit of a more eaſy proof, and we ſhall give you an Eſſay of it, ſince I have mentioned a thing that is not mere Imagination only: I ſay therefore, if any Perſon ſtrike thoſe Sounds which the Muſicians diſtinguiſh by theſe Letters, C, F, D, G, C, by theſe agreeable Intervals, altogether perfect, interchangeable, aſcending and deſcending with the Voice: Now this latter ſound C will be one Comma, or very ſmall portion lower than the firſt ſounding of C. Becauſe of theſe perfect Intervals, which are as 4 to 3, 5 to 6, 4 to 3, 2 to 3, an account is made in ſuch a Proportion, as 160 to 162. that is, as 80 to 81, which is what they call a Comma. So that if the ſame Sound ſhould be repeated nine times, the Voice would fall near the Matter a greater Tone, whoſe proportion is as 8 to 9. But this the Senſe of the Ears by no means endures, but remembers the firſt Tone, and returns to it again. Therefore we are compell’d to uſe an occult Temperament, and to ſing theſe imperfect Intervals, from doing which leſs Offence ariſes. And for the moſt part, all Singing wants this Temperament, as may be collected by the aforeſaid Computations. And theſe things we have offer’d to thoſe that have ſome Knowledge in Geometry.