193 
repetition of Mr. Christie's experiments , &c. 
produced, and those probably arose from errors in the adjust- 
ments themselves. 
The following effects were also noticed in the course of 
these experiments, viz. 
(ist.) In the different adjustments of the plate, it was found 
in general that the amount of the deviation from zero, due to 
rotation in the same direction, when the several points on the 
plate coincided with the fixed mark, was greater or less, ac- 
cording as the plate had been adjusted on the pin in the suc- 
cessive observations, with the several points coinciding with 
the fixed mark in the order o, 6 o, 120, 180, 240, 300, or in 
the order of succession 300, 240, 180, 120, 60 , o; although 
the whole amount of deviation due to rotation in opposite 
directions, was not sensibly affected by this circumstance. 
This effect is fully pointed out in Table I. and its probable 
cause suggested, 
(2nd.) One slozv revolution of the plate produced as much 
deviation as three or more turns ; quick revolutions were always 
attended with comparative trifling deflections of the needle. 
The plate retained the magnetic properties imparted to it by 
rotation, while remaining on the axis, round which it was 
made to revolve ;* but on its being placed horizontally on 
the ground, (which in this place was nearly in the plane of 
the magnetic equator), the effect was destroyed in the course 
of 10 or 15 minutes; implying that time is requisite for the 
complete developement of magnetism in the plate, as well as 
for the displacement of it, after it has been produced. 
* This is inferred from the observations of i|- hour only, during which time the 
direction of the daily variation needle was noted, and compared with that under thp 
influence of the plate. 
MDCCCXXVI. * C C 
