252 A. M. Mayer—Floating Magnets. 
appears only once, as nucleus respectively to 14, 15 and 180. 
This same power of the most stable nuclei to resist outside stress 
is shown in the configurations of the tertiary and quaternary 
classes, where the secondary 11 appears as nucleus to 21, 22, 
23 and 24. The secondary 18a persists in even a more marked 
manner asa nucleus. This 18a has the contour of that ve 
stable 7 (the only configuration possible with 7 magnets), whic 
forms its nucleus. Among the tertiaries 18a is the nucleus of 
306, 31, 32 and 33, while in the quaternaries it forms the inner 
nucleus of 46, 47, 48 and 49. The fact of the persistence of 4 
these stable forms as nuclei may be suggestive to chemists and 
erystallographers. 
It is here to be remarked that (as a general rule holding good 
in all the classes) of two configurations made up of the same 
number of magnets, that configuration is the more stable which 
has the least number of needles for its nucleus. 
Illustrations of Molecular Structure. (1.) Unstable Molecular 
Equilibrium.—That the molecules in a body may be in a state 
of unstable equilibrium, so delicately balanced that a slight 
extraneous action of pressure, of heat, light, ete., may cause a 
new molecular arrangement in the body, is shown in many 
facts. A few of the more familiar ones will answer for our 
purpose. Thus, quiet water, which remains liquid at a tem- 
perature of 10° C., or more, below 0° C., changes suddenly into 
ice when agitated ; and during this solidification its temperature 
rises. In like manner a supersaturated solution of disodium 
sulphate solidifies when a crystal of this substance is dropp 
into it. Another instance of a sudden change from an unstable 
to a stable molecular condition is shown when the yellow crys- 
tals of mercuric iodide change, on the touch of a glass rod, toa 
scarlet color with a perceptible motion of their particles. These 
and similar phenomena are illustrated by the change of unstable 
to stable configurations caused by vibration, shock, and varying 
conditions of stress. Thus, 5) changes into 5a; 6d into 6a; 
and 8¢ and 8d into 8a. 
(2.) Illustrations of the Expansion on Solidification, as shown 
by water, bismuth, antimony, cast-iron, etc., are readily given 
by the floating magnets. One volume of water at 0° C. expands 
on freezing into about one and one-tenth volume of ice. It 
happens that the area of 5b is greater than the area of 5a by 
about one-tenth ; so that the increase in area which takes place 
when the pentagon of 5a is changed into the square 50 may 
represent the increase in the volume of water when it changes 
into ice, 
It will be observed, on an examination of the diagrams, that 
of two configurations, formed of the same number of needles, 
that configuration which has the larger area has a magnet in its 
