VOL. XXXI.] PHILOSOPHICAL TRANSACTIONS. 495 



his thought of applying threads at half right angles in the common focus of a 

 telescope, to determine the differences of right ascension and declination of 

 any two stars, whose situation is such, that by their diurnal motion they follow 

 each other through the aperture of the telescope, so fixed as that the first of 

 them may pass over the centre of the glass, and move exactly along one of 

 the threads, while the interval of time between its transit, and that of the fol- 

 lowing star, is exactly measured by a pendulum clock, well adjusted to the 

 mean motion of the sun, or else to the revolution of the fixed stars, by which 

 the difference of right ascension is given ; as is the difference of declination, 

 by the time the following star takes to pass from one diagonal thread to the 

 other. By this manner of observing, Dr. Pound, and his nephew Mr. Bradley 

 did, in the last opposition of the sun and Mars, demonstrate the extreme mi- 

 nuteness of the sun's parallax, and that, by many repeated trials, it was not 

 more than 12^', nor less than 9". But considering that, in October next. 

 Mars would be again in opposition to the sun, about the 10th degree of 

 Taurus, but would not come very near any fixed star in Mr. Flamsteed's cata- 

 logue ; I was solicitous to see if there were any telescopic stars to which he 

 would very nearly approach ; and on the 28th of February last, the heavens 

 being very serene and clear in the evening, and Venus having nearly the decli- 

 nation in which Mars will move in October next, I fixed my telescope on her, 

 at 7^ 28*", equal time, and noted the moment she passed over the centre of 

 my glass, or rather the common intersection of the 4 cross hairs; and in half 

 an hour's time I noted 8 very conspicuous stars, 4 of which being within the 

 compass of one degree, fell very nearly in the said way of Mars; and from the 

 intervals of time I then observed, with their difference of declination from 

 Venus, I determined their right ascensions and declinations, as well as her 

 place from my tables, which by observation I found at this time needed no cor- 

 rection; all of them falling between the Qth and 10th degree of Taurus, with 

 very little latitude. But what confirmed me that all was right was, that on 

 Tuesday last, March 21 , Mercury appearing very fair, and newly past his greatest 

 elongation, I found by Senex's zodiac that he was nearly in the same parallel 

 that Venus had before described; and though the brightness of the crepusculum 

 effaced the smaller stars, yet in a quarter of an hour I had one past lO'^ more 

 southerly than the planet, which in less than 3™ of time was succeeded by 

 another, which was only l' more northerly than the former; when after an 

 interval of about 14 minutes of time, in which I was surprised to find the sky 

 so void of stars, the 4 beforementioned stars passed successively over my glass, 

 with the same interval of time in which I had seen them follow each other 

 on the 28th of February: on which I was desirous to try whether, if the place 



