275

Of Light and Colours.

(^crease as the Squares of the Distances^crease j and therefore the Light and Heat

of

f could not comprehend his Method were willingj? i>e satisfied of the Truth thereof otherwise, andjJ&htly judged; that if the Earth did move about theu,1 > it must: necessarily cause an apparent Motion inn y fixed Object at a Distance from it.

3 4 - Thus if ABCD represent the Orbit of the Earth,y? A and C the Place of the Earth at two oppositejA^es of the Year ; then a fixed Object at E will bee n from the Earth at A in the Line A E, which will° l nt out its apparent Place at G in the Concave Ex-y atl se of the Sky H I. But at the opposite Time of thep, e * r j it will be seen from the Earth at C in the Linejj which will project its Place in the Heavens at F.that while the Earth has passed from A by D to C,Object (though- in reality fixed) has appeared to°v e through the Space G F ; and the Angle which^asures this apparent Motion of the Object, viz. the(J'Sle A E.C is called the Paralladtic Angle or ParallaxAnnual Orbit-, because it measures the visible Ap-ar ance of the Diameter A C of the Earth’s Orbit at

he Object E.

jj $• This being the Cafe, it was applied to the fixedj ars , which they conclude would certainly have an^Parent Motion, or Parallax, provided an Instrumentbe made sufficiently exact to observe it, and this^° u |d be a satisfactory Demonstration of the Earth’sstL ti0n - Accordingly several Persons addressed them-\ £ v t0 d‘f cover a P ara -liax of the fixed Stars ; and in'Vi.v ar 172-:, the late

Hon.

Samuel Molyncux, Esqjb e ^ u an Instrument made by the accurate Mr. Graham *it to observe the bright Star in the Head of Draco asPtty e .^ ncar the Zenith. Professor Bradley also ob-'t along with him ; and from many Observations

^tb great Care, it appeared that the Star wastL s .Northerly 39 Seconds of a Degree in Septembertti March, just the contrary Way to what it oughtPP e ar by the annual Parallax of the Stars. That is*T 2 the

PlateXXXV;Fig. 2;