fe 
26 Prof. Tyndall on the Diamagnetic Force. 
tithetical in its manner of 1 atbleate the deportment of diamag- 
netic bodies is to be referre 
The next section of the inquiry imparted clearer knowledge 
as to the nature of diamagnetic action. ‘T'wo helices were so 
placed that the ends of the soft iron cores which fitted into them 
were about six inches apart from centre to centre; the helices 
were at opposite sides of the plane which touched the ends of the 
cores. A helix of copper wire was introduced, and within it a 
bismuth bar 63 inches long and four-tenths of an inch in diameter 
was see suspended, so that the ends of the bar were opposite 
o those of the soft iron cores. A current being sent through the 
helix, if whe bismuth bar within it were excited by the current it 
was probable that the nature of the excitement would manifest 
itself in the action of the magnets upon the diamagnetic body. 
By working delicately the most perfect mastery was obtained over 
the suspended bismuth ; when the current through the helix 
flowed in a certain direction the ends of the diamagnetic bar were 
repelled by the electro-magnets; when the current flowed through, 
the helix was reversed, and the same ends were attracted by the 
magnets. The same effect was obtained when, instead of revers- 
ing the helix current, the polarity of the two magnets was re- 
versed. On comparing the deflexions with those of soft iron, it 
was found that they were perfectly antithetical. The excitement 
which caused the ends of the iron bar to be repelled caused those 
of the bismuth bar to be attracted 
All these experiments point irresistibly to the conclusion that, 
whatever the ideal magnetic distribution in iron may be, a pre- 
cisely opposite distribution occurs in bismuth,—or, in other words, 
that the diamagnetic force is a polar force, but that the aaa 
is the reverse of magnetic polarity. If, however this be 
the bismuth bar, when the current circulates round it, must hae 
its two ends in different states; but if in different states, then if 
we make the two poles acting upon the ends of the bar alike, we 
ought to have attraction at one end and repulsion at the other,— 
the result of their opposing actions being that the bar must re- 
main undeflected. The decisive experiment has been made, and 
ie revolt 3 is in perfect accordance with the conclusion just expres- 
when both magnetic poles are of the same name they com- 
Bexaly peoralize each other. Following up this inductive rea- 
n, is easy to see that, if what has been stated be correct, 
when ve bring two magnets with poles of the same name to 
3 being: the same, then the repulsion of one end and 
other, instead of, as in the ae disposition, 
er, 2 AuEht to constitu ute a echanical cou 
muth bar, the direction of the for emanating from — 
