246 Mr. Squire on the Occultaiion of Aldebaran on July 16th, 



I was so fortunate as to get a good observation of the im- 

 mersion at this place; and which happened at ll h 56 ra 36 s, 3 

 mean solar time, or ll h 50 m 59 s, 4 apparent time. Now the 

 latitude of Epping is 51° 41' 41"*6 N., longitude 25 s -l E. of 

 Greenwich ; hence the apparent time of observation for the 

 meridian of the latter place is ll h 50 m 34 s, 3, but the com- 

 puted time in Moore's Almanack is stated at ll h 50 m 26% 

 making the absolute time of immersion at Epping later than 

 at Greenwich by about 8 s ; and this is very nearly the quan- 

 tity that would arise from the change in the lunar parallax. 

 So that the computed results in White's Ephemeris and 

 Moore's Almanack agreed (as usual) with the heavens to a 

 great degree of exactness. I regret that clouds prevented 

 my seeing the emersion, as I have no reason to doubt that the 

 same happy coincidence in the computed and observed times 

 would have been found to take place in this case as at the 

 immersion, always relying on the general accuracy of the 

 computations in the above and other Almanacks published 

 by the Stationers' Company. You will, Gentlemen, judge my 

 surprise at the concluding remarks of your Gosport corre- 

 spondent W. B., where, at page 234 of your last Number, he 

 gives what he calls the observed times of the immersion and 

 emersion of Aldebaran in this occupation ; and then unac- 

 countably comes suddenly to the conclusion, that " the ap- 

 parent time at Greenwich of the disappearance and re-ap- 

 pearance of Aldebaran, as given in White's Ephemeris and 

 Moore's Almanack, is nearly two minutes too fast; so that 

 the time deduced from what are considered accurate astrono- 

 mical computations does not in this instance, and indeed it 

 seldom does, agree with the time of observation." 



Now, W. B. makes the observed time of immersion at Gos- 

 port to be July 15th at 23 h 44 m ; and that of emersion, July 

 ] 6th at 3 l m 20 s ! But from a little consideration relative to this 

 phaenomenon, I am confident that one, and probably both, of 

 these observations is incorrect. However, let us see how 

 these numbers will stand the test of the most scrupulous com- 

 putation. For that purpose I will take the latitude of Gos- 

 port, as stated by Dr. William Burney, = 50° 47' 45" N. 

 and the longitude = 4 m 28 s W. of Greenwich, from which, 

 after a proper reduction of the latitude, and the moon's hori- 

 zontal parallax for polar compression, with other necessary 

 data, &c, I find that the immersion tookplace there July 15th 

 23 h 44 ra 6% and the emersion July 16th, h 34 m 16 s apparent 

 time, according to that meridian, instead of 23 h 44 m and 31 m 20 s 

 respectively, as given by your correspondent. So much for 

 the accuracy of W. B.'s observations made with the best 



power 



