152 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXIX.) 
effect, the axis of rotation must be perpendicular to the lines of force, /. e. the dip. It 
would even be possible to search for the direction of the lines of force, or the dip, by 
making the axis of rotation variable about the line of dip, adjusting it in two direc- 
tions until there was no action at the galvanometer, and then observing the position 
of the axis ; a double commutator would be required corresponding to the lines of ad- 
justment, but that is of very simple construction. 
^ 36. On the amount and general disposition of the Forces of a Magnet when associated 
with other magnets. 
3215. Prior to further progress in the experimental development by a moving wire of 
the disposition of the lines of magnetic force pertaining to a magnet, or of the physical 
nature of this power and its possible mode of action at a distance, it became quite 
essential to know what change, if any, took place in the amount of force possessed 
by a perfect magnet, when subjected to other magnets in favourable or adverse posi- 
tions ; and how the forces combined together, or were disposed of, i. e. generally, and 
in relation to the principle already asserted and I think proved, that the power is in 
every case definite under those different conditions. The representation of the magnetic 
power by lines of force (3074.), and the employment of the moving wire as a test of 
the force (3076.), will I think assist much in this investigation. 
3216. For such a purpose an ordinary magnet is a very irregular and imperfect 
source of power. It not only, when magnetized to a given degree, is apt by slight 
circumstances to have its magnetic power diminished or exalted, in a manner which 
may be considered for the time, permanent ; but if placed in adverse or favourable 
relations to other magnets, frequently admits of a considerable temporary diminution 
or increase of its power externally, which change disappears as soon as it is removed 
from the neighbourhood of the dominant magnet. These changes produce corre- 
sponding effects upon the moving wire, and they render any magnet subject to them 
unfit for investigation in relation to definite power. Unchangeable magnets are, 
therefore, required, and these are best obtained, as is well known, by selecting good 
steel for the bars, and then making them exceedingly hard ; I therefore procured 
some plates of thin steel 12 inches long and 1 inch broad, and making them as hard 
as I could, afterwards magnetized them very carefully and regularly, by two powerful 
steel bar-magnets, shook them together in different and adverse positions for a little 
while, and then examined the direction of the forces by iron filings. Small cracks 
and irregularities were in this way detected in several of them ; but two which Avere 
very regular in the disposition of their forces were selected for further experiment, 
and may be distinguished as the subjected magnets D and E. 
3217 . These two magnets were examined by the moving loop precisely in the man- 
ner before described (3133.), i. e. by passing the loop over one of the poles, observing 
the swing, removing it, and again observing the swing and taking an average of many 
results ; the process was performed over both poles at different times. The loop 
