350 Intelligence and Miscellaneous Articles. 
verse square of the distance is manifest through all the approximations, 
except a few of the last, the occasional irregularities observed being 
very inconsiderable ; so that when the magnets are very nearly approxi- 
mated in relation to their respective intensities, the increments in the 
forces begin to decline,—a circumstance of considerable importance 
in our endeavours to investigate the laws of magnetic attraction ; 
for it may be supposed that the inductive influence which thus begins 
to vary, may at last so far vanish, even before contact, that the abso- 
lute force, at near approximations, may in some instances, as already 
stated, be in an inverse SIMPLE RATIO OF THE DISTANCE™, and which was 
observed to happen with the bars marked d and e. For although the 
cylindrical counterpoise employed in these experiments did not admit 
of the forces being examined at nearer approximations than those 
marked in the table, yet by substituting one of large dimensions the 
forces may be carried on nearly up to the point of contact, so as to 
be estimated in terms of the preceding progression, since the degrees 
of attraction may be always compared and valued in grains of abso- 
lute weight.” 
‘In the following table are the results ofthe experiments so con- 
tinued with the magnets d and e ; the counterpoise being 1:0 inch in 
diameter, 1° of attraction corresponding to 10° of the former, and 
being equal to two grains of absolute weight :” 
Dissimilar Poles. 
D d | e 
0-4 | 6 | 18 
0-3 | 85 | 24 
0-2 | V3: | 36 
“Tt may be perceived in this table, that the corresponding forces 
at near approximations, do not materially vary from a simple inverse 
ratio of the distance.” 
« This deviation from the law of the inverse square of the distance 
observed in all the near approximations of the magnets may happen 
either in consequence of the distant polarities having passed a certain 
limit, or otherwise from the inductive action not going on with the 
same freedom at some point approaching saturation. The latter 
would seem to be extremely probable ; for it has been already shown, 
that when two dissimilar polarities are opposed to each other, their 
free action becomes more or less neutralized.” ——T7vaus. of Royal So- 
ciety of Edinburgh, vol. xi. p. 310—312. W. J. A. 
ON THE AURORA OF THE 18TH NOVEMBER LAST. 
Communicated by Professor Rigaud. 
During the beautiful aurora which took place on the 18th of last 
November, it is remarkable that Mr. Sturgeon was not able to see 
any of its light excepting in the north. Dr. Robinson, in the last 
number of the Phil. Mag. (p.236.), has drawn an important conclu- 
sion from this circumstance; it may be right, therefore, to state 
* The Italics and capitals in this passage are our Correspondent s.—Eprr. 
