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( 6jy )
nary, with reSpect to the Motion I am now considering ; I will Set down a Sew more Instances of Such, from which you may be able to judge how near it may be possible from these Observations, to determine with what Velocity Light is propagated.
ct Perfei Bayero was 23'' more Northerly at the beginning of January than in July. Hence the Maximum would be 40", 2. «, CaJJiopea was 34'' more Northerly about the End of ‘December than in June, Hence the Maximum would be 40", 8. # 'Draconis was 39" more Northerly in the beginning of Sept cm* her than in March; hence the Maximum would be 40", 2. Capella was about 16'' more Southerly in Augufi than in February; hence the Maximum would be about 40". But this Star being farther from my Zenith than those I have before made use of, I cannot fo well depend upon my Observations of it, as of the others; because I meet with fome fmall Alterations of its Declination that do not seem to proceed from the Caufe I am now considering.
I have compared the Observations of Several other Star?, and they all conSpire to prove that the Maximum is about 40" or 41". I will thereSore SuppoSe that it is 40"# or (which amounts to the Same) that Light move?, or is propagated as far as from the Sun to us in 8' 13". The near Agreement which I met with among my Observations induces me to think, that the Maximum (as I have here fixed *it) cannot differ So much as a Second from the Truth, and therefore it is probable that the Time which Light Spends in passing from the Sun to us, may be determined by thefe Observations within 5" or 10" ; which is fuch a degree of exactnefs nc we can never hope to attain from the Eclipses of s/’ piter's Satellites, F
( 65<S )
Having thus found the Maximum, or what the greatest Alteration of Declination would be in a Star placed in the Pole of the Ecliptick, I will now deduce from it (according to the foregoing Hypothesis) the Alteration of Declination in one or two Stare, at such times as they were actually obferved, in order to See how the Hypothesis will correfpond with the Phenomena through all the Parts os the Year.
It would be too tedious to Set down the whole Series of my Observations ; I will therefore make Choice only of fuch as are most proper for my preSent Pur-poSe, and will begin with thoSe of y 'Draconis.
This Star appeared farthest North about September 7th, 17x7, as it ought to have done according to my Hypothesis. The following Table shews how much more Southerly the Star was found to be by Observation in Several Parts of the Year, and likewise how much more Southerly it ought to be according to the Hy-pothefis.