344 Magnetical Experiments and Observations 
at which the needle traversed this meridian, going to the west- 
ward, was about five o’clock in the afternoon, and going east- 
ward about six o’clock in the morning. The greatest easterly 
deviation happened at about ten o’clock in the morning, and the 
greatest westerly about the same time in the evening, observing 
that we here speak of the true easterly and westerly points, and 
not of the magnetic east and west ; we ought, perhaps, rather 
to have said, that the greatest westerly magnetic bearing was 
at ten o’clock in the morning, and the greatest easterly at ten 
o’clock in the evening, for the mean variations being at Port 
Bowen about 124° westerly, the true and magnetic points were 
nearly reversed. The daily motion of the sun was obviously a 
primary cause of this daily variation, because it increased as the 
power of the sun increased ; but it was very considerable even 
while the latter made its whole daily revolution below the hori- 
zon ; and when it afterwards never sunk below the horizon, the 
character of the daily variations was preserved, the only change 
having been in the amount which was considerably greater in 
the latter case than in the former. It is the opinion, also, both of 
Captain Parry and of Lieutenant Foster, that some part of the 
observed changes was owing to the influence of the moon ; the 
mean daily motion having been found uniformly greater at the 
time of conjunction than in quadrature or opposition. 
In the experiments before alluded to by Mr Barlow, the 
needle was, by means of his neutralizing magnets, held at vari- 
ous points of the compass, in order, if possible, to trace out the 
direction of the force which produced the daily change in the di- 
rection of the needle ; and he found a line about 16° to the 
west of the magnetic north, in which, when the needle was 
placed, there was no daily motion ; or, at least, the motion was 
then at its minimum. Similar experiments were made at Port 
Bowen by Lieutenant Foster ; and having carefully neutralized 
the needle, instead of a daily motion of 5° and 6°, he now ob- 
tained, in some positions, a variation of 50° and 60°, decreas- 
ing, as in Mr Barlow’s, towards a minimum. In the present 
case, the line of no daily motion was about 84° from the meridian, 
and the order of the motion on each side of this line, as in those 
above referred to, was reversed, the needle on one side of this 
line passing to the right, and on the other side to the left, at the 
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