22^ Royal Astronomical Society. 



of this importance. Under these circumstances, a representation 

 of the case was laid before the Lords Commissioners of the Admi- 

 ralty, who immediately ordered a fair copy of the observations to 

 be made j and the same was by them presented to this Society in 

 December 1832. It was in consequence of this gift that the author 

 was induced to draw up the present memoir. 



Mr. Baily first gives an account of the number and state of the 

 instruments at the Observatory, the clocks, &c.: and it appears that 

 for four years, at least, after Dr. Halley was appointed to his situa- 

 tion, he had only a 5>-feet transit instrument wherewith to carry 

 on his observations. This is the first instrument of the kind erected 

 there, and is described as " a curious telescopic instrument, fitted 

 to an axis, and adjusted with screws to revolve in the plane of the 

 Tneridian." It is evident, therefore, that Halley could at that period 

 take nothing but transits. On the erection of the mural quadrant, 

 however, in 1725, he was enabled also to take the zenith distances 

 of the stars. He mnde observations likewise with two or three move- 

 able telescopes with which he was furnished. And much confusion 

 occurs, in the manuscript books, from the circumstance that the ob- 

 servations with all these different instruments are recorded exactly 

 alike, so that there is nothing to guide the reader as to xuhich instru- 

 ment has been used in the observation. 



The state of his clocks also is represented as being very confused 

 and irregular ; and the numerous stoppages they experienced, either 

 in the act of being wound up, or from being suffered to run down, 

 through absence or neglect, render it extremely difficult to deduce 

 any very accurate results from the transit observations at such 

 periods : an inconvenience which is felt, even to the very end of his 

 labours. 



Dr. Halley 's observations were principally directed to the moon 

 and planets : and with this object in view he usually observed such 

 stars as were nearly on the same parallel of declination as those 

 bodies, and differing from them very little in right ascension. Such 

 observations therefore may, even now, be made available for deter- 

 mining the positions of those moveable bodies at those periods, and 

 thus tend to perfect their theory. But with respect to any accurate 

 information relative to the absolute position of the fixed stars, the 

 author considers that it would be difficult, if not impossible, to ob- 

 tain it : and that the most that can be expected from the observa- 

 tions would be the determination of the relative positions of some 

 adjacent stars ; neither does he consider that the observed stars are 

 in sufficient number to warrant the expense and trouble of attempt- 

 ing such a measure. 



After entering into an explanation of these and other modes of 

 observing adopted by Dr. Halley, the author proceeds to notice some 

 of the most remarkable phaenomena recorded in the manuscript vo- 

 lumes. He states, that although there are many observations of the 

 superior planets, yet none of them are very near the time of their 

 opposition to the sun. There are also several observations of Venus 

 and Mercury; but not a single observation of the eclipses of Jupiter s 



