422 PHILOSOPHICAL TRANSACTIONS. [aNNO 1747-8. 



the position of the parts of my sector : but considering how firmly the arc, on which 

 the divisions or points are made, is fastened to the plate in which the wire is 

 fixed that lies in the focus of the object-glass ; I saw no reason to apprehend that 

 any change could have happened in the position of that wire and those points. 

 The suspension therefore of the plummet being the most likely cause, from 

 whence I conceived any uncertainty could arise ; and the wire of which had been 

 broken 3 or 4 times in the first year of my observations: I attempted to examine 

 whether part of the before-mentioned apparent motions might not have been 

 owing to the different plumb-lines that had been made use of. In order to de- 

 termine this, I adjusted a particular point of the arc to the plumb-line, with all 

 the exactness I could ; and then, taking off the old wire, I immediately hung on 

 another, with which the same spot was again compared. I repeated the experi- 

 ment 3 or 4 times, and fully satisfied myself that no sensible error could arise 

 from the use of different plumb-lines ; since the various adjustments of the same 

 point agreed with each other, within less than half a second. ,\! 



Having then, from such trials, sufficient reason to conclude, that these second 

 unexpected deviations of the stars, were not owing to any imperfection of my 

 instrument ; after I had settled the laws of the aberrations arising from the mo- 

 tion of light, &c. I judged it proper to continue my observations of the same 

 stars; hoping that, by a regular and longer series of them, carried on through 

 several succeeding years, I might at length be enabled to discover the real cause 

 of such apparent inconsistencies. 



As I resided chiefly at Wansted, after my sector was erected there in the year 

 1727, till the beginning of May 1732, when I removed from thence to Oxfbrd. 

 I had, during my abode at Wansted, frequent opportunities of repeating my ob- 

 servations ; and thereby discovered so many particulars relating to these pheno- 

 mena, that I began to gviess what was the real cause of them. 



It appeared from my observations, that during this interval of time, some of 

 the stars near the solstitial colure had changed their declinations Q" or 10'' less, 

 than a precession of 50" would have produced ; and at the same time, that others 

 near the equinoctial colure, had altered theirs about the same quantity more, 

 than a like precession would have occasioned : the north pole of the equator 

 seeming to have approached the stars, which come to the meridian with the sun, 

 about the vernal equinox and the winter solstice ; and to have receded from those 

 which come to the meridian with the sun, about the autumnal equinox and the 

 summer solstice. 



When I considered these circumstances, and the situation of the ascending 

 node of the moon's orbit, at the time when I first began my observations ; I 

 suspected that the moon's action on the equatorial parts of the earth might pro- 

 duce these effects : for if the precession of the equinox be, according to Sir Isaac 



