C ad 7 1 
being moved or othcrways affected, he argues, that 
the common Air does not produce the Sound, but 
a more fubtil Fluid better proportioned to the Or- 
gans of Hearing : Here he runs into a Detail of the 
Principles of the Chords and Tones of Mufic, and 
makes a new and curious Comparifon between the 
principal Colours in the Rays of Light, and the fore- 
faid Fluid, which is more or lefs fubtil in the Air, 
fome Particles of which are only capable of being 
moved to exprefs low Tones, others higher, and fo 
on fucceftlvely, as far as the Compafc of Mufic 
reaches j juft as the Light is compofed of certain 
kinds of Rays, fome of which produce Red, fome 
Green , &c. This being fuppofed, fays he, it may 
be conceived, that every Tone will move the Fluid 
that is proper to itfelf ; and by that means the Ear 
may receive at once the Imprellions of every Fluid, 
as the Eye receives the Impulsions of feveral coloured 
Rays at the fame Inftant. He adds to this, by way oF 
Reafoning, that when a Engle String of an Inftru- 
ment is touched, though the generality of Mankind 
can diftinguilh but One Tone, which he calls the 
fundamental Sound , yet People accuftomed to Har- 
mony can diftinguilh, befides, an Ohlave, a Fifth, and 
a Third , covered by this fundamental Tone ; for the 
Offave is half that Sound, or the Produce of half the 
String 5 the Fifth is the Produce of Two-thirds, and 
the Third is the Produce of Four-fifths of the fame 
String. 
He proceeds to rcafon upon this in an agreeable' 
Manner, and concludes hits above-mentioned Com- 
parifon to this Purpofe : Thus there are in the vi- 
brated String all the Harmonies or Chords at once, 
which . 
