534 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Using these formulae Dr Struve finds for the epoch 1874-0, 1 /^ = 52 0, 6 
and sin ydO — 0 o, 208, giving the period of revolution of the pole of the 
orbit round the pole of Neptune equal to 1734 sin y years. 
Comparing the present observations with Dr Struve’s in 1890, the 
changes of N and I in this interval and the value of \fs for the mean date 
1896-2 are found. 
(Dr Struve) 1890-4 N=185°-27 I = 119°T6 
1901-9 N = 187°-45 I = 117°-44 
Hence in 11'5 years dN = + 2°T8, dl — — 1°*7 2 ; and the annual changes of 
N and I are 
d$= +0°-190 dl= — 0°*150 
for 1896"2, Dr Struve’s result for 1874"0 being 
dN = +0°-148 dl= -0°-165. 
Thus, for the mean date 1890-2, 
N=186°*36 1=1 1 8° *30 
i/q= 41°*9 sin ’225, 
and the time of revolution = 1000 sin y years. 
Comparison of the values of \js for 1874-0 and 1890-2 may be used to 
determine the value of y and of the position of Neptune’s equator. 
We have 
M t N 1= 52°-6 N 2 M 2 = 41°-9 
M 1 N 1 N 2 = 122°-0 M 2 N 2 N 1 = 61°-7 
]S\N 2 = 3 0 -58. 
Solving the triangles, we find 
EM 2 N 2 = y = 2 L 0, 2 
M 2 EN 2 = 47°‘2 
N 2 E= 1 9°*2. 
Thus the inclination of the orbit of the satellite to Neptune’s equator 
is 21 0, 2, while the longitude of the node and the inclination of Neptune’s 
equator to the Earth’s equator are 2O5°"0 and 132°"8. 
This value of the inclination implies a rotation of the pole of the 
satellite’s orbit in about 580 years. 
It follows that the inclination of Neptune’s equator to the ecliptic, which 
agrees closely with Neptune’s orbit round the Sun, is about 27°. 
These results are in good agreement with those obtained from the 
Greenwich observations by Prof. Dyson and Mr Edney (M.N., vol. lxv.). 
