405 
iron arising from its rotation. 
Whatever are the effects produced on the iron by its revo- 
lution, so far from these effects being of the transient nature 
which we must suppose them to be on this hypothesis, 
they appear to have been quite permanent, that is, so long 
as the iron remained in the same position. The following 
observation will show the small changes which took place 
during 12 hours. 
In order that the needle might be quite free to move, it 
was suspended in a balance of torsion by a brass wire, of 
the same diameter as the finest gold wire used for transits, 
free from torsion, 21.15 inches long. The plane of the plate 
was in the plane of the secondary to the equator and meri- 
dian, its centre in latitude 0° longitude 180° ; and it was fixed 
to a wooden axis passing through its centre perpendicular to 
its plane : the ends of this axis, which revolved with the 
plate, being made of brass, that I might ascertain whether 
the effect was independent of friction on the plate itself. The 
plate was made to revolve in contrary directions, as usual, 
and the directioTi of the north end of the needle noted, when 
the point 180° on the plate coincided with the upper part of 
a plane parallel to the meridian, and passing through the 
plate’s centre. After having made the plate revolve so that 
its upper edge moved from west to east, and noted the direc- 
tion of the north end of the needle when 180° coincided with 
the above plane, it was made to revolve from east to west, 
and 180° being again brought to coincide with this plane, the 
direction of the north end of the needle was noted at diffe- 
rent times for more than 12 hours, the plate remaining 
stationary during that time. 
