2g4 PHILOSOPHICAL TRANSACTIONS. [ANNO 1787. 



appears necessary to examine what this may amount to. Accordingly, on a fur- 

 ther calculation he finds a correction of Q" in declination, and IM in right as- 

 cension. 



As therefore Mercury passed with 23' 1" more north declination than a Orionis, 

 and passed through a part of the medium that lifted him up less; it therefore 

 gave him less north declination than it did to a, and therefore apparently dimi- 

 nished the real difference; hence Q" must be added to the apparent difference 

 23' 2", making it 23' 8^' difference of declination : and as Mercury was lifted up 

 less than a, he would not so soon come to the middle wire by IM as he should 

 have done, he therefore came too late by IM, which must be subtracted from 

 the time of Mercury's passage the 23d of Sept. which will increase the time in 

 which he preceded a Orionis; that is, 18^ 43™ 42'.4 increased by IM will be- 

 come 18^ 43"" 43^5 difference of right ascension. 



Having thus determined that the 23d Sept. 1786, a. m. at 5^^ 22"^ 34\9 mean 

 time. Mercury preceded a, Orionis 18'' 4 3"^ 43^5, and had then a more northern 

 declination by 23' 8''. But according to Dr. Maskelyne's Catalogue of 34 stars, 

 the right ascension of a Orionis reduced to the time when he was observed is 

 85° 54' 12''. Now as the whole circle of the sphere makes a revolution in the 

 time that x Orionis makes one turn, which is 23^ sS'" 4M, then from this 

 deduct 18^ 43"" 43*.5, remains 5^ 12"^ 20\6, for the time that a Orionis pre- 

 ceded Mercury in right ascension ; but if a ran the whole rotation = 36o° in 

 23^ 56"™ 4M, what portion of it will be run in 5^ 12"" 20\6 = 18740\6 ? 



But 24^ = 86400 seconds, and 36o = 1296OOO seconds : 



Say then, as 86400' : 18740'.6 :: 1296OOO" : 281 109" = 78=» 5' 9" 



But, according to Dr. Maskelyne's select Catalogue, the right ascension of « Orionis 



for Sept. 30, 1786', was, (which add) 85 54 12 



The r. asc. of Mercury at the time of observation was therefore l63 59 21 



According to Dr. Maskelyne's select Catalogue « Orionis had declination north, cor- 

 rected for precession 7° 21' 8".8 



The sum of aberration and nutation from Connoissance des Temps 4- 8.4 



Gives the correct declination north of « Orionis ., 7 21 17 .2 



To which add that Mercury passed more north 23 8 



Mercury's declination therefore was 7 44 25 .2 



The result. 



1786, Sept. 23, A. M. "^ Mprrnrv'* \ '"'S^' ascension l63 59 21 



at 5" 22"" 35' m. t. \ ^^^'^^^"v » ^ declination north 7 44 25 



XXXIJ^. A Remarhahle Case of numerom Births, with Observations. By 



Maxwell Garthshore, M. D., F. R. S., and A. S. p. 344. 

 Copy of a Letter from Dr. Blane, Physician to his Majesty's Navy, and to St. 



Thomas's Hospital, f. r. s., to Dr. Garthshore, Physician to the British Lying-in 



hospital. Dated Sackville-street, June 22, 1786. 



