VOL. XLV.] PHILOSOPHICAL TRANSACTIONS. 42Q 



is the reason why the series of observations of those is so imperfect^ as sometimes 

 to leave a chasm for several years together. But notwithstanding this, I doubt 

 not but on the whole, they will be found sufficient to satisfy the astronomer 

 of the general correspondency between the hypothesis and the phenomena, in the 

 several stars; however different their situations are, with respect to the cardinal 

 points of the equator. 



As I made more observations of y Draconis, than of any other star; and it 

 being also very near the zenith of Wansted; I will begin with the recital of some 

 of them. The point on the limb with which this star was compared, was 38° 25' 

 from the north pole of the equator, according to the numbers of the arc of my 

 sector. The first column, in the following table, shows the year and the day of 

 the month, when the observations were made; the next gives the number of 

 seconds that the star was found to be south of 38° 25'; the 3d contains the alter- 

 ations of the polar distance, which the mean precession, at the rate of one de- 

 gree in 714- years, would cause in this star, from the 27th day of March 1727, 

 to the day on which the observation was taken ; the 4th shows the aberrations of 

 light; the 5th, the equations arising from the beforementioned liypothesis; and 

 the (5th gives the mean distance of the star from the point with which it was 

 compared, found by collecting the several numbers, according to their signs, in 

 the 3d, 4th, and 5 th columns, and applying them to the observed distances con- 

 tained in the 2nd. 



If the observations had been perfectly exact, and the several equations of their 

 due quantity; then all the numbers in the last column would have been equal; 

 but since they differ a little from one another; if the mean of all be taken, and 

 the extremes be compared with it, we shall find no greater difference, than what 

 may be supposed to arise from the uncertainty of the observations themselves ; it 

 no where amounting to more than ly. The hypothesis therefore seems, in this 

 star, to agree extremely well with the observations here set down; but as I had 

 made above 300 of it, I took the trouble of comparing each of them with the 

 hypothesis: and though it might have been expected that, in so large a number, 

 some great errors would have occurred ; yet there are very few, viz. only eleven, 

 that differ from the mean of these so much as 2"; and not one that differs so 

 much as 3". This surprising agreement therefore, in so long a series of observa- 

 tions, taken in all the various seasons of the year, as well as in the different posi- 

 tions of the moon's nodes, seems to be a sufficient proof of the truth both of this 

 hypothesis, and also of that which I formerly advanced relating to the aberrations 

 of light; since the polar distance in this star may differ, in certain circumstances, 

 almost a minute, viz. 56^''', if the corrections resulting from both these hypo- 

 theses are neglected; whereas, when those equations are rightly applied, the 

 mean place of the star comes out the same, as nearly as can reasonably be ex- 

 pected. 



