56 Royal Astronomical Society. 



ROYAL ASTRONOMICAL SOCIETY. 

 (Continued from vol. xix. p. 584.) 

 Nov. 12, 1841. — The following communications were read : — 

 I. On the Longitude of Dr. Lee's Observatory at Hartwell. 

 The longitude of this observatory was assumed from various au- 

 thorities to be 3 m 20 s * 6 west from the Royal Observatory at Green- 

 wich, by the late Mr. Epps, for some time after his arrival at Hart- 

 well. These authorities appear to have been as follows : m s 

 Capt. Smyth, by means of two trips with a chronometer "I „ -1 - 



from Bedford Observatory J 



By the moon's culminations as computed by Mr. Riddle 19 - 9 



Mr. Epps, by chronometers 21*7 



Ditto 20-7 



Mean longitude 3 20-6 



The mean of these determinations was naturally supposed by Mr. 

 Epps to be very near the truth. In October 1838 this mean result 

 was found, however, to differ considerably from the difference of 

 meridians as determined by twelve chronometers, taken by Mr. Dent 

 from the Royal Observatory (which was 3 m 24 s, 46). It was evi- 

 dent, therefore, that there was either an error of nearly four seconds 

 of time in the longitude of Hartwell, as previously assumed, or in 

 the observations made there on this occasion to determine the error 

 of the clock with which the chronometers were compared. A care- 

 ful recomputation of the observations, as recorded in the Hartwell 

 transit books, was therefore made, and the result (as far as the re- 

 ductions were concerned) was found to be correct. 



A reference was then had to Aylesbury church spire, the position 

 of which had been determined by the Trigonometrical Survey. This 

 was done by means of an estimated distance of the spire from the 

 Hartwell Observatory, taken from a county survey, and the observed 

 azimuth of the former from the observatory. This gave a result 

 (3 m 23 s- 07) differing 2 S *5 of time from Mr. Epps's former determi- 

 nation, and l s, 5 from that obtained from Messrs. Arnold and Dent's 

 chronometers, and was therefore far from being satisfactory. 



In the following January another series of results was obtained 

 by means of ten chronometers, which were taken by Mr. Dent as 

 before, from the Royal Observatory to Hartwell, on the 6th of that 

 month, and the comparisons made with the transit clock at the latter 

 place on the same day. The chronometers were brought back to the 

 Royal Observatory on the 9th following. The difference of meri- 

 dians by these observations was 3 m 24 s- 06. 



Other results were also obtained by means of chronometers taken 

 from the Royal Hospital Schools at Greenwich to Hartwell Obser- 

 vatory ; and, in reference to these results, as well as to those before 

 obtained, Mr. Epps observes, in a letter to Mr. Fisher, "The results 

 agreeing so well with the former, I think we may conclude that 

 3 m 24 s, 2 (as you have already noticed) is extremely near the truth. 

 This may be called the mean result of thirty chronometrical deter- 

 minations. I may remark to you, that my observations for time are 

 made with as much attention as possible to the state of the transit 



