$62 Mr. Christie on the diurnal deviations of the 
In this position of the needle, the morning deviation is at 
first towards the east, and afterwards towards the west, the 
same as when the north end of the needle pointed north, the 
needle tending towards the same point in the two cases, but 
in contrary directions. This is what we might expect from 
a simple change in the direction of the terrestrial force, but 
the observations which I shall presently describe, clearly 
point out both a change of direction and of intensity. 
Having ascertained the nature of the changes which take 
place with the north end of the needle towards the north, and 
also towards the south, I proceeded to make observations 
with the north end in other directions. For this purpose I 
had prepared another compass, in order that I might observe 
at different points at the same time. This compass was placed 
in my garden, that it might be completely out of the influence 
of the magnets adjusted to the other needle, and likewise 
that I might be able to notice, whether, as Mr. Barlow had 
found, the deviations were in contrary directions in the two 
cases, when the north end had the same, or nearly the same, 
direction in both. The observations were not, in this point 
of view, very conclusive, because although the deviations 
differed in many respects, in some they agreed, and likewise 
because the magnets were not adjusted in the same manner 
in the two cases ; those within doors being in the line of the 
dip, and those to the other needle being in the meridian, on 
the same horizontal table as the compass. The points at 
which the observations were made within doors were the 
north end at N 28° W and N 49 0 W ; and with the other 
needle at N 55 0 W. After continuing to make these obser- 
vations carefully for some days, it occurred to me that I 
