502 PROFESSOR CHALLIS, ON THE DETERMINATION OF THE LONGITUDE 



I proceed now to state by what means the signal-times were converted into sidereal times 

 of the respective Observatories. Two methods were employed, which for distinction I will 

 call method (A) and method (B). In the former, the errors of the transit-clocks were 

 determined by the ordinary processes employed at the two Observatories, excepting that the 

 assumed apparent Right Ascensions of the stars observed for clock-errors at Cambridge, after 

 being taken from the Nautical Almanac, were corrected by small quantities derived from the 

 results of Greenwich observations, so that their assumed mean R. A. 1853,0 are the same as 

 those adopted for the year at Greenwich. The following are the. stars which were observed 

 for clock-errors on the nights of May 17 and May 18, with, their assumed apparent Right 

 Ascensions. 



At Greenwich, May 17. 



Name of Star. 



Apparent R. A. 

 A. m. t. 



Aldebaran 4.27.28,11 



I Virginis 12.48.12,98 



rj Bootis 13.47.42,40 



£ Herculis 16.35.46,28 



At Cambridge, May 17. 



A. m. $. 



Aldebaran 4.27.28,11 



a Orionis 5.47.11,75 



I Crateris 11.12. 0,12 



/3 Leonis 11.41.34,14 



fi Corvi 12.26.41,28 



Spica 13.17.28,32 



At Greenwich, May 18. 



Name of Star. Apparent B. A. 



A. m. t. 



§ Leonis 11. 6.17,59 



£ Crateris 11.12.0,11 



/3 Leonis 11.41.34,13 



/3 Corvi 12.26.41,27 



§ Virginis 12.48.12,98 



rj Bootis 13.47.42,39 



k Virginis 14. 5. 4,78 



£ Herculis 16.35.46,30 



ij Ophiuchi 17. 1.58,47 



a Herculis 17. 7.58,10 



a Ophiuchi 17.28. 8,03 



At Cambridge, May 18. 



A. m. s. 



/3 Leonis 11.41.34,13 



Spica 13.17.28,32 



a Ophiuchi 17.28. 8,03 



In method (B), a list of stars having been previously prepared, clock-errors were deduced 

 from the observations of those that were observed at both Observatories on the same night, 

 the same values of their apparent Right Ascensions being employed for that purpose. The 

 following are the stars so used. Their apparent R. A., which it is unnecessary to subjoin, 

 were derived from the Greenwich Twelve-year Catalogue. 



Stars observed at Greenwich, 

 and Cambridge, May 17. 



Aldebaran 

 38 Virginis 

 $ Virginis 

 g Virginis 

 53 Virginis 

 6l Virginis 

 I 2 Virginis 



Stars observed at Greenwich 

 and Cambridge, May 18. 



P Virginis 



/3 Leonis 

 y Virginis 

 38 Virginis 

 8 Virginis 

 g Virginis 

 53 Virginis 

 6l Virginis 



32 Ophiuchi 

 r\ Ophiuchi 

 X Herculis 

 a Ophiuchi 



