204 -Mr. Christie’s remarks on the repetition 
since in longitude 90°, the deviations in south latitude are 
greater than the corresponding ones in north latitude, and 
the reverse takes place in longitude 270°; but as the differ- 
ences are very small, I, at the time of making the obser- 
vations, rather attributed them to errors in the adjustment, 
than to any other cause. 
When the centre of the plate was in the secondary to the 
equator and meridian, and its plane a tangent to the sphere, 
I had found the deviation due to rotation so small, that it 
might be considered to vanish : at Port Bowen, however, 
the absolute deviation was so great, that in some parts of this 
circle the deviation due to rotation became sensible ; and it 
would appear that the locus of the points where this devia- 
tion vanishes is a line of double curvature, passing from the 
south pole on each side, a little north of the secondary, down 
to its intersection with the equator, and then a little south of 
the secondary to the north pole. The signs which I have 
prefixed to the deviations in Table IV. of Mr. Foster’s 
observations, indicate the course of this curve. 
The whole of the results in Mr. Foster’s observations 
perfectly agree with the law which I have given in my 
Paper as embracing all the phenomena dependant upon 
rotation, and even the differences which I have noticed 
between my own observations and these, are precisely such 
as we should expect, according to this law, to be observable 
in a change of the complement of the dip from 20° to 2 0 . 
The results obtained by the repetition of my experiments 
at Port Bowen, prove that the phenomena depending on 
rotation are by no means unimportant as connected with the 
practical problem of correcting the attraction of a ship on 
