1868.] 



Proceedings of the Asiatic Society. 



95 











Cm 1 Chi 



Chi 



Group 



o A 



g.a 

 ■a g 



<-* CO ' 



CfH -P fl 



O © O 





a^ 



.si 



© 

 © © 



>T3 u 



3 error 

 e culmina 

 r a pair 

 distances. 



O 



h 



© P< 



P 



© O 





® -■> 





d O 



3 2P°£ 



3 &0 





8 &c 





• r-l Ci_i 



6J0 O 



rO S3 § d 



c8 





g 





O rg 



HI CS ■+= IS] 



2 





*25 « 





h3 W 



Ph 



P4 







ft 



m s 



S 



• 



Moon Culminations, •• .. 



29 



6 



10 5064. 



+ 679 



+ 1-26 



Lunar Zenith Distances to times 













by Astronomical Clock, • . 



67 



6 



10 50-53 



3-04 



0'37 



Lunar Zenith Distances to times 













by Chronometer, .. 



34 



6 



10 51-88 



331 



0-57 



Final Longitude 

 East of Greenwich, 



f In time, 

 [ In Arc, 



6 h 10 m 50-92 s ± 0'30 s 

 92° 42' 43"-8 ± 4"*5 



It will be seen that the probable error by a single culmination is 

 more than double tbat by a pair of zenith distances, a curious circumstance 

 which could scarcely have been anticipated, and which shows that in 

 tropical latitudes a few nights of observstions of lunar zenith distances 

 will give as satisfactory a result as observations of culminations extend- 

 ing over several months, for not more than 8 culminations can usually 

 be observed in a month, and several of these may be lost if the weather 

 is cloudy and unfavorable. 



The latitude was deduced from observations of 17 stars situated to 

 the north of the zenith and 20 stars to the south, the means of the two 

 groups differing by only 0".08. The final result is — 



North lat. 11° 41' 12", 85° 0"11. 

 The probable error is computed on the assumption that there is no 

 constant error in the Tables in the Nautical Almanac, from which 

 the stars' places were taken. 



The Observatory was situated on the highest point of Chatham 

 Island at an altitude of 73 feet above the sea and about 30 feet to the 

 south of the upper road from the Sepoy Barracks on the west 

 of the Island to the officers' quarters on the east. It is 150 feet 

 NE. of the east wall of the Sepoy Barracks, 130 feet NW. of the 

 nearest corner of the house built for the Overseer of the Department 



