1853. 
WEEKLY EVENING MEETING, 
Friday, January 21. 
WiuiamM Pots, Esa., M.A., F.R.S., Treasurer and Vice-President, 
in the Chair. 
Proressor FarapDay, 
Observations on the Magnetic Force. 
Inasmucu as the general considerations to be brought forward had 
respect td those great forces of the globe, exerted by it, both as a 
mass and through its particles, namely, Magnetism and Gravitation, 
the attention was first recalled briefly to certain relations and diffe- 
rences of the two which had been insisted upon on former occasions. 
Both can act at a distance, and doubtless at any distance : but whilst 
gravitation may be considered as simple and unpolar in its rela- 
tions, magnetism is dual and polar. . Hence one gravitating particle 
or system cannot be conceived to act by gravitation, as a particle or 
system, on itself; whereas a magnetic particle or system, because 
of the dual nature of its force, can have such a self relation. Again, 
either polarity of the magnetic force can act either by attraction or 
repulsion; and not merely so, but the joint or dual action of a 
magnet can act also either by attraction or repulsion, as in the 
case of paramagnetic and diamagnetic bodies: the action of gravity 
is always that of attraction. As a further consequence of the diffe- 
rence in character of the powers, little or no doubt was entertained 
regarding the existence of physical lines of force* in the cases 
of dual powers, as electricity and magnetism; but in respect of 
gravitation the conclusion did not seem so sure. As some further 
relations of the sun and the earth would have finally to be sub- 
mitted, the audience were reminded, by the use of Arago’s idea, 
of the relative magnitude of the two; for, supposing that the centres 
of the two globes were made to coincide, the sun’s body would 
not only extend as far as the moon, but nearly as far again, its 
bulk being about seven times that of a globe which should be 
girdled by the moon’s orbit. 
For the more careful study of the magnetic power a torsion 
balance had been constructed, which was now shown and its mode 
of operation explained. The torsion wire was of hard drawn pla- 
tinum, 24 inches in length, and of such diameter that 28.5 inches 
* Proceedings of the Royal Institution, June 11, 1852, p. 216, also Philosoph. 
Mag. 4th Serics, 1852, III. p. 401. 
