LINES OF MAGNETIC FORCE — MAGNETIC POLARITY. 
49 
that due to conducting- power, and differing far less from them, than they do from 
other metals not magnetic. 
3153. The amount of lines of force (and of the force represented by them) appears, 
therefore, to be equal for equal spaces occupied by tin, iron, and platina under the 
circumstances; for the difference in result is in no proportion to the ordinary mag- 
netic difference, and only as the conducting power. This agrees with the conclusion 
before arrived at, that, for air, water, bismuth, oxygen, nitrogen, or a vacuum, the 
lines of force are the same in amount, except as they are more or less concentrated 
in the substance across which they pass (2807.), according as it is more or less com- 
petent to conduct ( 2797 .) or transmit the magnetic force. 
3154. Such a conclusion as that just arrived at, brings on the question of what is 
magnetic polarity, and how is it to be defined ? For my own part, I should understand 
the terra to mean, the opposite and antithetical actions which are manifested at the 
opposite ends, or the opposite sides, of a limited (or unlimited) portion of a line of 
force (2835.). The line of dip of the earth, or a part of it, may again be referred to 
as the natural case; and a free needle above or below the part, or a wire moving 
across it (3076. 3079.), will give the direction of the polarity. If we refer to an 
entirely different and artificial standard as the electro-magnetic helix, the same 
meaning and description will apply. 
3155. If the term polarity have any meaning, which has reference to experimental 
facts and not to hypotheses only, beyond that included in the above description, I 
am not aware that it has ever been distinctly and clearly expressed. It may be so, 
for I dare not venture to say that I recollect all I have read, or even all the conclu- 
sions I myself have at different times come to. But if it neither have, nor should 
have, any other meaning, then the question arises, is it correctly exhibited or indi- 
cated in every case by attractions and repulsions, i. e. by such like mutual action of 
particular bodies on each other under the magnetic influence ? A weak solution of pro- 
tosulphate of iron, if surrounded by water, will, in the magnetic field, point axially; 
if in a stronger solution than itself, it will point equatorially (2357. 2366. 2422.). The 
same is true with stronger cases. We cannot doubt it will be true even up to iron, 
nickel, and cobalt, if we could render these bodies fluid in turn without altering their 
paramagnetic power, or if we had the command of magnets and of paramagnetic and 
diamagnetic media, stronger or weaker at pleasure. But in the case of the solutions, 
we cannot suppose that the weaker has one polarity in the stronger solution and 
another in the water. The lines of force across the magnetic field have the same 
general polarity in all the cases, and would be shown experimentally to have it, by 
the moving wire (3076.), though not by the attractions and repulsions. 
3156. Here, therefore, we have a difference in the two modes of experimental indi- 
cation ; not merely as to the method, but as to the nature of the results, and the very 
MDCCCLII. 
H 
