daily variation of the horizontal and dipping needles , &c. 335 
From the above results, although the experiments were 
not made under such favourable circumstances as I could 
wish, we may draw some very curious, if not important con- 
clusions ; such, for instance, as the following. That while 
the north end of the needle is directed to any point from the 
south to NNW, its motion during the forenoon is towards 
the left hand ; advancing therefore to some point between the 
NNW and north ; and while it is directed towards any point 
between the north and SSE it passes to the right hand, that is 
still to some point between the north and NNW ; the south 
end of the needle at the same time passing of course to some 
point between the south and SSE ; so that it would seem 
that there ought to be some direction between those limits, 
viz. between the N and NNW, and the S and SSE, in which 
the daily motion is zero, or at least a minimum, ( see Plate 
XXIII. ) : but whether this is a fixed direction during the year, 
or whether it has any vibratory motion as the sun changes 
its declination, or even during his daily course, is a question 
which cannot be decided without a much longer course of 
experiments than those I have here the honour to present. 
It is also questionable, whether the direction of this line of 
no daily variation is the same in different parts of the world ; 
a point on which I hope to obtain some information in the 
course of the present year. Mr. Foster,* of H. M. S. Griper, 
* I am already highly indebted to this Gentleman for the accurate and satisfac- 
tory observations he made during the recent voyage of H. M. S. Conway, under 
the command of Captain Basil Hall, on the method I had the honour to propose 
for correcting the local attraction of vessels ; and it is with great pleasure that I 
find he has been directed by the Admiralty to continue his attention to them in the 
present voyage of the Griper. My best thanks are also due to Captain Hall, for 
the facilities he afforded in the instance above mentioned, and for the judgment 
