312 PHILOSOPHICAL TRANSACTIONS. [aNNO 1728. 



became stationary, or was farthest north or south, when they passed over the 

 zenith at 6 o'clock, either in the morning or evening. He perceived likewise, 

 that whatever situation the stars were in, with respect to the cardinal points of 

 the ecliptic, the apparent motion of every one tended the same way, when they 

 passed the instrument about the same hour of the day or night; for they all 

 moved southward, while they passed in the day, and northward in the night; 

 so that each was farthest north when it came about 6 o'clock in the evening, 

 and farthest south when it came about 6 in the morning. 



Though Mr. B. afterwards discovered, that the maxima in most of these stars 

 do not happen exactly when they come to the instrument at those hours, yet 

 not being able at that time to prove the contrary, and supposing that they did, 

 he endeavoured to find out what proportion the greatest alterations of declina- 

 tion in different stars bore to each other; it being very evident, that they did 

 not all change their declination equally. Mr. B. before observed, that it appeared 

 from Mr. Molyneux's observations, that y Draconis altered its declination about 

 twice as much as the forementioned small star almost opposite to it; but exa- 

 mining the matter more particularly, Mr. B. found that the greatest alteration 

 of declination in these stars, was as the sine of the latitude of each respectively. 

 This made him suspect that there might be the like proportion between the 

 maxima of other stars; but finding that the observations of some of them would 

 not perfectly correspond with such an hypothesis, and not knowing whether the 

 small difl^erence met with, might not be owing to the uncertainty and error of 

 the observations, he deferred the further examination into the truth of this 

 hypothesis till he should be furnished with a series of observations made in all 

 parts of the year; which might enable him not only to determine what errors 

 the observations are liable to, or how far they may safely be depended on, but 

 also to judge, whether there had been any sensible change in the parts of the 

 instrument itself. 



On these considerations, Mr. B. laid aside all thoughts at that time about the 

 cause of the forementioned phaenomena, hoping that he should the easier dis- 

 cover it, when better provided with proper means to determine more precisely 

 what they were. 



When ihe year was completed, he began to examine and compare his obser- 

 vations; and having pretty well satisfied himself as to the general laws of the 

 phaenomena, he then endeavoured to find out the cause of them. He was 

 already convinced, that the apparent motion of the stars was not owing to a 

 nutation of the earth's axis. The next thing that ofi^ered itself, was an altera- 

 tion in the direction of the plumb-line, with which the instrument was con- 

 stantly rectified ; but this, upon trial, proved insufficient. He then considered 



