Mr. Christie's remarks , &c. 
201 
to their investigation than I could have at all contemplated, 
knowing how fully his time must be otherwise occupied. 
To those who have previously read my Paper on this sub- 
ject in the Transactions, the general accordance of the results 
in the foregoing tables, and those which I obtained, must be 
quite manifest; as however they exhibit some differences, 
I shall here briefly point out the agreement between the 
original experiments and this repetition of them, and 
likewise those discordances, and at the same time indicate 
what I consider to be the cause of some of these apparent 
discrepances. 
In all the observations which I made, the deviations of the 
needle due to the rotation of the plate, depended both in 
extent and character, not upon the situation of the plate with 
respect to the axis and equator of the horizontal needle 
itself, but upon its situation with reference to the axis and 
equator of an imaginary dipping needle having its centre 
coinciding with that of the horizontal needle ; and this ap- 
pears most clearly to have been the case at Port Bowen. 
In every instance the direction of the deviation due to 
rotation was the same at Port Bowen as I had found it here, 
the relative positions of the plate and needle, and the direc- 
tion of rotation being the same in the two cases. 
When the plane of the plate was in the secondary to the 
equator and meridian, I had found that the mean deviation 
due to rotation in latitude o was -{- i° 36' and in latitude 
90, — o° 45' : at Port Bowen the corresponding deviations 
were -f- 14 0 14' and — 6° 28', which are as nearly in the same 
ratio as we could expect, considering the irregularities which 
take place in the individual observations in the latter case. 
*Dd 
MDCCCXXVI. 
