1908-9.] 
Motion of Neptune’s Satellite. 
517 
XXXIII. — Motion of Neptune’s Satellite. By David Gibb, M.A., B.Sc. 
Communicated by Prof. Dyson. 
(MS. received 10th June 1909. Read 12th July 1909.) 
1. Neptune’s satellite was discovered by Mr Lassel of Liverpool in 
1846. This satellite differs from the other planets and satellites, except 
those of Uranus, in the direction of its motion, which is from east to west. 
After the satellite had been observed for a few years, it was pointed out 
by Mr Marth that the node and the inclination of its orbit were slowly 
changing. These changes were explained by Tisserand and Newcomb as 
arising from the spheroidal shape of Neptune. The observations prior to 
1892 have been discussed by Dr Struve in the Memoir es de V Academie 
Imperials des Sciences de St Petersbourg, vii e serie, tome xlii. No. 4. Since 
then a large number of valuable observations have been made at American 
observatories, especially by Prof. Barnard, and at Greenwich Observatory. 
The former were obtained visually with a position micrometer, the latter 
from photographs. Some of the American observations have already been 
discussed by Mr Hall (A.J., xii. 22, xix. 65), Mr Brown (A.J., xx. 134), and 
Prof. See ( A.N. , 153), and the Greenwich observations are discussed in 
the Monthly Notices (vols. lxv. and lxviii.) by Prof. Dyson and Mr Edney. 
In this paper I propose to discuss some of the visual observations made 
since 1892. Since 1899 the Connaissance des Temps has given tables which 
facilitate the calculation of the ephemeris of the satellite. These tables are 
based on the elements of Dr Struve. As no such tables are published 
previous to the above date, I have formed them from 1892 to 1898 inclusive, 
using the same elements. 
2. The elements given by Dr Struve are :-= - 
Epoch 1890*0. 
a = 1 6" *27 1 
u = 234°*42 
n= 61°-25748 
N = 185°T5 + 0°T48(£ - 1890) 
1= 1 19° ‘35 — 0°T65 t - 1890), 
where a is the distance of the satellite from the planet for the mean distance 
of the planet from the Earth. 
n = mean daily motion 
u = longitude of satellite 
X = longitude of node 
I = inclination of orbit 
referred to the Earth’s 
equator and the equinox 
of date. 
