titution of Great Britain, March
4, 1881, on "Elasticity Viewed as possibly a Mode of Motion"; Thomson and
Tait's "Natural Philosophy," second edition, part 1, Sec.Sec. 345 viii. to 345
xxxvii.; "On Oscillation and Waves in an Adynamic Gyrostatic System" (title
only), _Proc_. R.S.E. March, 1883.]

The drawings (Figs. 1 and 2) before you illustrate two such material
systems.[1] The directions of rotation of the fly-wheels in the gyrostatic
system (Fig. 2) are indicated by directional ellipses, which show in
perspective the direction of rotation of the fly-wheel of each gyrostat.
The gyrostatic system (Fig. 2) might have been constituted of two
gyrostatic members, but four are shown for symmetry. The inclosing circle
represents in each case in section an inclosing spherical shell to prevent
the interior from being seen. In the inside of one there are fly-wheels, in
the inside of the other a massless spring. The projecting hooked rods seem
as if they are connected by a spring in each case. If we hang any one of
the systems up by the hook on one of its projecting rods, and hang a weight
to the hook of the other projecting rod, the weight, when first put on,
will oscillate up and down, and will go on doing so for ever if the system
be absolutely unfrictional. If we check the vibration by hand, the weight
will hang down at rest, the pin drawn out to a certain degree; and the
distance drawn out will be simply proportional to the weight hung on, as in
an ordinary spring balance.

[Footnote 1: In Fig. 1 the two hooked rods seen projecting from the sphere
are connected by an elastic coach-spring. In Fig. 2 the hooked rods are
connected one to each of two opposite corners of a four-sided jointed
frame, each member of which carries a gyrostat so that the axis of rotation
of the fly-wheel is in the axis of the member of the frame which bears it.
Each of the hooked rods in Fig. 2 is connected to the framework through a
swivel joint, so that the whole gyrostatic framework may be rotated about
the axis of the hooked rods in order to annul the moment of momentum of the
framework about this axis due to rotation of the fly-wheels in the
gyrostat.]

[Illustration: FIG. 1]

[Illustration: FIG. 2]

Here, then, out of matter possessing rigidity, but absolutely devoid of
elasticity, we have made a perfect model of a spring in the form of a
spring balance. Connect millions of millions of particles by pairs of rods
such as these of this spr