334 
Mr. Christie’s theory of the 
From these it appears, that the maximum westerly varia- 
tion occurred about i h 30 m P. M. from which time the needle 
deviated towards the east until nearly 9 P. M.; after which a 
small deviation to the west took place during the night, until 
an early hour the next morning ; from which time the devia- 
tion was easterly until nearly 9 A. M. when the easterly 
deviation attained its maximum, this maximum being consi- 
derably to the east of the minimum westerly variation in the 
evening. This excess appears to be different for different 
seasons of the year. The mean of the winter months, 
November, December, January, gives it very nearly nothing, 
the whole amount of daily variation being 6 7 4 6 ". For 
February, March, April, it is 3' 23", or not quite a third of 
the whole variation 10' 36". For May, June, July, it is 
4' 33 " , or more than a third of the daily variation 12' 09". 
And for August, September, October, it is 2' 26", or not quite 
a fourth of n' 25", the whole daily change. In this table, 
the mean daily variation for different months is rather less 
than that deduced by Canton. This arises from the exclu- 
sion, in the mean, of those days on which the variation was 
irregular, and on which, in general, the maximum west was 
considerably greater, and the minimum less, than on those 
days on which it was regular. 
The observations at Port Bowen have been so recently 
published, that it is unnecessary for me here to point out the 
nature of the results ; and any remarks I may have to make 
on them, I shall reserve until I have given the experiments 
with which I propose to compare them. 
In order to determine how nearly the changes in the direc- 
tion at Fort Enterprise, in London, and at Port Bowen, might 
