196 Mr. G. A. Schott on the 
II. A sphere of infinite mass, and a ring of an infinite, 
practically a large, number of electrons ; 
,tan,r- =7r. 
3-r-/3 2 — 2n 
III, A sphere whose mass is purely electromagnetic, that is 
Zv 2 e 2 
equal to ^-^r, and a ring of few electrons ; 
v 2 e 2 b 1 
25?I~6' 
IV. A sphere whose mass is purely electromagnetic, and a 
ring of many electrons. 
The following conclusions can be drawn from these 
curves : — 
(1) In similar sytems both paramagnetism and dia- 
magnetism, as measured by the specific moment, are 
proportional to the volume. 
(2) Increasing the mass of the sphere increases para- 
magnetism, and diminishes the critical radius. 
(3) Increasing the radius of the ring increases para- 
magnetism. 
(4) Increasing the number of electrons in the ring 
diminishes paramagnetism and increases the critical 
radius. 
§28. We must now study the numerical values of the 
moments given by our formula? and compare them with the 
values found by experiment. For this purpose it is most 
convenient to use the atomic susceptibilities of the elements; 
St. Meyer* gives a table referred to one gram atom per 
litre with a unit for k ecjual to 10~ 6 . If we take 10~ 24 gr. to 
be the mass of the atom of hydrogen, \\ e find the number of 
atoms in one c.c. of a solution or powder containing one gram 
per litre to be 1 21 ; hence we must multiply Meyer's numbers 
by 10- 27 . 
Again, the weak iron amalgam studied by Nagaoka (§ 21) 
contained 4.10 20 atoms per c.c. and had a susceptibility "0013. 
This gives p=3'2 .10~ 2i for iron. Meyer's table gives 
p= — 2'0 . 10~ 28 for bismuth ; all other elements have inter- 
mediate values with the possible exception of erbium> which 
Meyer estimates to be four times as magnetic as iron w 7 hen 
pure, corresponding to p = l'3 . 10~ 23 . The greatest para- 
* L. c. lxix. p. '2o3, 
