COMMENTÄTIO ASTRONOMICA. 169 



« -vations of bolh matle upon Ihesame days, at different seasons of Ihe year ) Ihis plainly 

 « proved , ihat Ihe apparent motiou of the stars was not occasioned by a real nulation, 

 « since if Ihal had beeu Ihe cause , the alteration in bolh stars -vvould have been near 

 a equal. 



« The greal regularify of the observalinns left no rootn fo doubr , but that Ihere was 

 « some regulär cause Ihat produced this unexpected motion, which did not depend on 

 « the, uncertainly or variely of the seasons of the year. Upon comparing the observa- 

 « lions with each other, it was discovered, that in both the forementioned stars the 

 « apparent difference of declinaiion from the maxima , was always nearly proportional 

 « to the versed sine of the sun's distance from the equinoctial points. This was an indu- 

 « ceracnt to Ihink, that the cause, whatever it was, had some relation to the sun's si- 

 « tiiation wilh respect to those points. But not being able to frame any hypothesis at 

 « that time , sufficienl to solve ail the phaenomena , and being very desirous to search 

 « a little farther into this matter, I began to think of erecting an instrument for my 

 « seif at Wansted , that ha-ving it always at band , I might with the more ease and cer- 

 « tainty enquire into the laws of this new motion. The consideration likewise of being 

 « able by another instrument, to confirm the truth of the obseryations hitherlo made 

 « with Mr. Molyneux's was no small inducement to me ; but the chief of all was the 

 « opportunity I should thereby have of trying , in what manner other stars were afTected 

 « by the same cause, whatever it was. For Mr. Molyneux's instrument being origi- 

 « nally designed for observing y Draconis (in order , as I said before, to Iry whelher 

 « it had any sensible parallax) was so contrived , as to be capab'e of but little altera- 

 « tion in ils direction , not above seven or eight minutes of a degree : and there being 

 « few Stars within half that distance from the zenith of Kew , brighl enough to be well 

 « observed, he could not, with bis instrument, throughly examine how this cause afiec- 

 « ted stars differently situated with respect to the equinoctial and solstitial points of the 

 « ecliptick. 



« These considerations determined me ; and by the contrivance and direction of the 

 « same ingenious person , Mr. Graham, my instrument was fixed up August 19, 1727. 

 « As I had no convenient place where I could make use of so long a telescope as Mr. 

 « Molyneux's, I contented myself with one of but little more than half the lenglh of 

 « bis (viz. of about 12^ fect , his being 24| ) judging from the experience , which I had 

 « already had , that this radius would be long enough to adjust the instrument to a 

 « sufficienl degree of exaclness, and I have had no reason since to change my opinion : 

 « for from all the trials I have yel made I am very well satisfied, that when it is care» 

 « fully rectified , its Situation may be securely depended upon to half a second. As 

 « t}ie place , where my instrument was to be hung , iu some measure determined its ra- 



Y « dius , 



