216 NOTICES OF THE MEETINGS [June 11, 
WEEKLY EVENING MEETING, 
Friday, June 11. 
Sir Cuaries Fettows, Vice-President, in the Chair. 
Proressor FARADAY, 
On the Physical Lines of Magnetic Force. 
On a former occasion, (Jan. 23, 1852, see p..105) certain lines 
about a bar magnet were described and defined (being those which 
are depicted to the eye by the use of iron filings sprinkled in the 
neighbourhood of the magnet), and were recommended as expressing 
accurately the nature, condition, direction, and amount of the force 
in any given region either within or outside of the bar. At that 
time the lines were considered in the abstract. Without departing 
from or unsettling any thing then said, the enquiry is now entered 
upon of the possible and probable physical existence of such lines. 
Those who wish to reconsider the different points belonging to these 
parts of magnetic science may refer to two papers in the first part of 
the Phil. Trans. for 1852 for data concerning the representative lines 
of force, and to a paper in the Phil. Mag. 4th Series, 1852, vol. iii. 
p- 401, for the argument respecting the physical lines of force. 
Many powers act manifestly at a distance; their physical nature 
is incomprehensible to us: still we may learn much that is real and 
positive about them, and amongst other things something of the 
condition of the space between the body acting and that acted upon, 
or between the two mutually acting bodies. Such forces are pre- 
sented to us by the phenomena of gravity, light, electricity, mag- 
netism, &c. These when examined will be found to present 
remarkable differences in relation to their respective lines of forces ; 
and at the same time that they establish the existence of real physical 
lines in some cases, will facilitate the consideration of the question as 
applied especially to magnetism. 
When two bodies, a, 6, gravitate towards each other, the line in 
which they act is a straight line, for such is the line which either ~ 
would follow if free to move. The attractive force is not altered, 
either in direction or amount, if a third body is made to act by gravi- 
tation or otherwise upon either or both of the two first. A balanced 
cylinder of brass gravitates to the earth with a weight exactly the 
same, whether it is left like a pendulum freely to hang towards it, or 
whether it is drawn aside by other attractions or by tension, what- 
ever the amount of the latter may be. A new gravitating force may 
be exerted upon a, but that does not in the least affect the amount of 
power which it exerts towards 6. We have no evidence that time 
