18 REPOHT— 1869. 



Oil the Heat of the >Stars^\ B>i Willi.vji Hugoins, i'^.E.*b'. 



On the Loin/itude of the Eadcliffe Observatory, Oxford, as deduced from Me- 

 ridional Ohservations of the Moon, made at Greenwich and Oaford, in the 

 years 1864-68. By the llov. E. Main, M.A., F.R.S., F.B.A.S. 



As the luoon has been observed for several years at the Eadclifte Observatory 

 with the Carringiou Trausit-cu-cle, Mr. Main has tliought it desirable to make, by 

 means of the observations as compared with those made .at Greenwich, a determi- 

 nation of the longitude of the Observatory. The whole number of observations 

 employed is 217, and include all that were made on the same day at the two Ob- 

 servatories from the year 1864 to 1868, both inclusive. 



The following Table gives thelresults deduced from the observations of each year, 

 together with the final result of the whole of the observations, and the probable 



errors :- 



The longitude of the observatory which has been assumed since the year 1841 

 5m 28(3^ which is less than that given above by l^'OS. This assumed longitude 

 was determined by the late Rev. Ei Sheepshanks, by chronometers carried back- 

 wards and forwards between Greenwich and Oxford, and though, unfortunately, 

 the details have never been published, there is no doubt that the determination was 

 most trustworthy. Assuming its correctness, and considering the difi'erence be- 

 tween it and the lunar determination to be due to error in the observation of the 

 moon's limb, this error would amount very closely to 0*'04 to be divided between 

 the two observatories. 



Now, as it is known that a personal equation peculiar to the moon's limb does 

 occasionally exist, to the amount of two or three-tenths of a second, it is probable 

 that an error much smaller in amount may affect all transits of the limb, and the 

 preceding investigation will show that in the case of the Greenwich and Oxford 

 observers it is very small. 



On the Discordance usually observed betiveen ike results of Direct and Reflexion 

 Observations of North Polar Distance. By the Rev. E. Main, M.A., F.R.S., 

 F.R.A.S. 



In this paper the author attempts to put in a, clear light the origin of the sing:ular 

 difference which has been generally observed, in the use of the mural or the transit- 

 circle, between the results of direct and reffexiou observations. After attributing to 

 the present Astronomer Royal the merit of originally organizing the system of re- 

 ffexion observations as now practised, and of keeping his attention steadily fixed 

 upon the discordance in question, Mr. Main remarks that the Greenwich obser- 

 vations are, both from the frequency and goodness of the observations, best cal- 

 culated for exhibiting tlie nature of the errors. He takes then for examination the 

 star-observations of I860 and 1866, which are pecxdiarly suitable for the investi- 



* Vide Proceedings of the Eoynl Society, vol. xvii. p. 309. 



