314 P. E.. Chase on Mechanical Polarity. 
copper ring (a), fixed to horizontal supports (6) (c), on which it 
can be rapidly rotated by a wheel (2) and pinion (¢), the sup- 
ports being relieved by friction-wheels (f). The outer diameter 
of the ring is 6 inches at each edge, and 6,3, inches in the mid- : 
dle; the inner diameter 5 inches; the thickness 14 inches. The — 
axle opposite to the gearing (9), is hollow, to allow the insertion — 
of a brass rod (k), which supports a compass (2) horizontally in — 
the interior of the ring. The compass is not shielded by a glass, 
and it is therefore easily affected by aerial currents, If the te : 
is made to revolve around the compass needle, the N. pole ot 
the needle is deflected in a direction opposite to the motion of — 
the top of the ring. ; ae 
r my special purpose, I replaced this copper ring by @ 
wooden one of the same dimensions, and prepared a number of 
dises (4) (J), in the form of semicircles and circular segments, 
fitted so that they could be fixed, in different vertical positions, 
in the compass bux, above the needle. Causing the wheel 1 
: rotate, with the axis variously placed, I tried the following ex 
. periments :— 
A. Single disc, or multiple and parallel dises. 
a. Axis in magnetic meridian. 
7. When the dise was in the meridian, the currents produced ; 
= 
a slight tendency in the needle’ to move in the same direction as 
the upper part of the ring. 
8. When the dise was in the equator, the slight tendency Me: 
9. When the disc was inclined to the meridian, there was a 
marked polarity, perpendicular to the disc. = 
b, Axis in magnetic equator. - 
10. The dise being placed in the meridian, there was no dis- 
_turbing current. : “3 
11. Placing the dise equatorially, the needle was still undis- 
turbed 
12. But when the dise was inclined to the meridian, the cur- 
rent-polarity was parallel to the disc. 
¢. Axis 45° from magnetic meridian. : é 
13. In nearly all positions of the disc, there appears to be a 
disposition in the needle to move from the axis of thering. But 
when the dise is in or very near the meridian, there is a slight 
tendency towards the axis. 
____In order to imitate more closely the earth’s principal thermal 
-Fadiation-planes, which are all theoretically parallel with the 
