and on the computed Times of it. 247 



power of his achromatic telescope ! By changing the above 

 computed instants into Greenwich time, it will be seen that 

 the variation in the moon's parallactic angle caused the abso- 

 lute time of immersion at Gosport to be l m 52 s earlier; and 

 that of emersion l m 3 s later than at Greenwich, which, from 

 the visible position of the moon with respect to the star, &c, 

 must eventually have been the case. 



For the sake of further comparison I will here give another 

 example or two. The emersion of Aldebaran, December 9th, 

 1829, P.M., was observed at Greenwich to take place at 

 6 h 46 m 49 s apparent time, and the computed result, according 

 to Moore's Almanack, is 6 h 47 m 7 s ; difference 18 s . The 

 immersion was not observed. 



Again; on January the 6th, 1830, A.M., Aldebaran was 

 observed at Greenwich to disappear behind the dark part of 

 the moon at 3 h 37 m 34 s *5 apparent time, but the computed 

 immersion in Moore's Almanack is 3 h 37 m 26 s , differing from 

 the observed time only 8£ s . Clouds prevented the emersion 

 being observed. 



I wish I could have added more examples, but the above 

 may suffice to show that the computations in White's Ephe- 

 meris and Moore's Almanack are much nearer the truth than 

 W. B. would seem disposed to allow. On the 6th and 15th 

 of October opportunities may again offer for W. B. to try 

 his hand in this way ; and in order to avoid errors in future, 

 let me advise him not only to use his best pcnoer; but also his 

 best clock, as correct time is allowed on all hands to be of 

 consequence in observations of this kind ! 



At Epping the immersion was observed with an achro- 

 matic, and a power of 50 only ; the star seemed to rest upon 

 the moon's disc some seconds before it disappeared. 



It is to be hoped that astronomers will pay attention to the 

 occultation of Aldebaran on the 6th of next month, which 

 will be visible in the S. and S.W. parts of England; as good 

 observations on this important occultation, if made in places 

 whose situations are accurately established, may afford some 

 useful data for determining the true figure of the earth. If 

 micrometrical measurements of the moon's diameter could be 

 taken at the time, they would be of use. 



I take this opportunity of observing that the d in iR of 

 Aldebaran and the moon, on July 15th, as given in the Nau- 

 tical Almanack, is not correct : instead of 23 h 21 m 4 s , it should 

 be 23 h 21 m 56 s . 



I remain, Gentlemen, yours respectfully, 



Thomas Squire. 



P.S.— 



