24 



ASTRONOMICAL OBSERVATIONS 



several determinations. The next reliable time observations are on February 20, 

 1854, which gave E = — 4'' 42°" 5P.4 at 7" 56° (mean time); the daily rate is 

 accordingly — 0'.42 (gaining), and the chronometer error on mean time for the 

 several occultations becomes: — 



1853. December 12, U'' 



1854. January 8, 18 

 " February 4-5, 1 



13, 20 



£' = _4i' 42™ 21'. 7 



—4 42 33.3 



—4 42 44.8 



—4 42 48.2 



Occultation of Saturn. 



of Mars. 



That the rate of the pocket chronometer during the above times was. uniform is 

 proved by the comparisons with the other chronometers; between December 12 

 and January 8, 2143 had a gaining rate on the pocket chronometer of 1'.9, between 

 the latter date and February 5 it was 2'.3, and between the last date and February 

 13 it was 2'.2. The true rate of 2143 is, therefore, — 2'.2 — O'A = — 2^6. 



The following table contains the observed times of the several phases of the 

 occultations of Saturn and ring: — 



The method of reduction used is that of finding the time of true conjunction in 

 right ascension, and the notation the same as given in vol. II. of Sawitsch's Treatise 

 on Practical Astronomy (German edition, by Dr. W. C. Goetze, Hamburg, 1851). 

 Hansen's interpolation formula was used. The tabular Nautical Almanac places 

 and data have been corrected, when practicable, from the Greenwich observations. 



Longitude from the Observations of the Occultation of Saturn's Ring. 

 December 12, 1853. 

 Immersion, last contact of ring 7'' 48™ 20'. 1 Sidereal time 



Emersion, 



or 19'^ 04": 

 8 21 55.0 [ at Van Rensselaer 19 37 



20'. 8 

 50.3 



) Approx. Gn 

 j wicli mean ti 



Green - 

 me. 



From the Greenwich Nautical Almanac, as corrected from the Greenwich observations : 



At immersion, a C . . .3^ 39™ 02'. 59 

 At emersion . . . . 3 40 -08.92 



(Correction to Nautical Almanac — 0'.22) 

 At immerson, S <L . . . +18° 12' 55".l 

 At emersion . . . . 18 18 08.9 



(Correction to Nautical Almanac — 5".0) 

 At immersion, horizontal parallax (L 54' 07".l 

 At emersion 54 06.8 



(Correction +0".3 according to Adams.) 

 At immersion, semidiametcr <L . . 14' 45". 5 

 At emersion . . . . . 14 45.4 



(Correction — l".l according to Oudeman's 

 Astronomische Nachr. No. 1202.) 



At immersion, o 12 . . 3^ 39™ 09'. 11 



At emersion . . . . 3 39 08.71 



(Correction to Nautical Almanac +0'.15.) 

 At immersion 5 >2 . . +17° 14' 26".3 



At emersion . . . . 17 14 25.2 



(Correction to Nautical Almanac — 8".9.) 



Horizontal parallax h 

 Semidiametcr ^ 



1".0 

 9".2 + l".0 



Mean time of 6 , Greenwich 19^ 07™ 39'. 3 



