306 
To find, therefore, the magnetic intensity 
which would produce the same effect on the 
orientation of the molecule as would be pro- 
duced by rotating the body at the angular 
velocity Q, all we have to do is to equate 7’ and 
T’. This gives 
4 A 1Q 
é pH sin 6 = sin d-Can (1-45 7 cos? ) 
or 
H = .0(1 4520050) =2%0 (1452 cosa) 
be 2@ e 2a 
The values of Q experimentally attainable are 
so small in comparison with any possible 
values of w» that the last term is negligible. 
Hence we have for any molecule in the body, 
whatever its orientation and whether it con- 
tains one or more orbits, 
or 
if N denotes the angular velocity in revolu- 
tions per second. : 
If therefore only one kind of electricity, with 
fixed ratio of mass to charge, is in orbital revo- 
lution in the molecules of a magnetic body, 
rotating it with the angular velocity NV revolu- 
tions per second is equivalent to putting it in 
a magnetic field of strength H, the intrinsic 
magnetic intensity of rotation, such that, with 
great precision, 
H/N = 4a = 
If we assume that negative electrons alone 
are in orbital revolution, the value of the sec- 
ond member of this equation, according to 
well known experiments on electrons in slow 
motion, is — 7.1 < 10-7 electromagnetic units, 
‘and H/N should be equal to this quantity and 
identical for all magnetic substances. If posi- 
tive electrons also participate the magnitude of 
H/N should be smaller. 
If the Ampéreian currents consist in the 
motion of actual matter, so that the molecules 
of magnetic substances have angular momen- 
tum, an ordinary magnet or electromagnet 
itself should behave to some extent like a gyro- 
SCIENCE 
[N. 8. Vou. XLVIIT. No. 1239 
scope when set into rotation. The first to see 
this, as well as the first to see any relation be- 
tween magnetism and angular momentum, ap- 
pears to have been Maxwell, who constructed 
apparatus for experiments on the subject as 
early as 1861. 
In Maxwell’s apparatus an electromagnet 
was pivoted in a circular frame in such a way 
as to be free to rotate about a horizontal line 
through its center of mass and perpendicular 
to its magnetic axis. With the magnetic axis 
making an angle @ with the vertical, the frame 
was rotated at high speed about a vertical 
axis, also passing through the magnet’s center 
of mass, and observations were made for a 
change in @, stability having been secured by 
suitable adjustments of the principal moments 
of inertia. No change could be detected, but 
only rough observations were possible. 
In the experiments on magnetization by ro- 
tation Maxwell’s electromagnet is replaced by 
each one of the countless multitude of molec- 
ular magnets of which the magnetic body is 
constituted, and the total change in the orien- 
tations of all these magnets with reference to 
the axis of rotation of the body is determined 
magnetically.’ 
th2xe--—--- - 9 --387ef-- - - —-- --— — --— — ee 
! 
' 
emt Bees lon : 
we i zezeraeaneral CoiL 
i) Hy 
2 bfkem. Ire RODB 3 —1Stem,. 
& 
| steme- 
O/TTTITIT ITLL COWL 
bye -- -- -— == rece 84. bim- - --— — ----- 
Fig. 3. 
Two series of experiments have been made, 
both with Mrs. Barnett’s assistance, and by 
methods as different from one another as pos- 
sible. The first series of experiments was made 
3I have learned very recently from a footnote in 
John Perry’s Spinning Tops that-he made experi- 
ments on this subject, with the same idea in mind, 
but without success, many years ago. 
