in one second, and then multiplying the product into the
square of the distance of the satellite from its primary. Finally, we
compute the moment of momentum of the sun due to its rotation. This we
obtain by multiplying the angle through which the sun turns in one
second by the whole mass of the sun, and then multiplying the product by
the square of a certain line of prodigious length, which depends upon
the details of the sun's internal structure.

If we have succeeded in explaining what is meant by the moment of
momentum, then the statement of the great law is comparatively simple.
We are, in the first place, to observe that the moment of momentum of
any planet may alter. It would alter if the distance of the planet from
the sun changed, or if the velocity with which the planet rotates upon
its axis changed; so, too, the moment of momentum of the sun may change,
and so may those of the satellites. In the beginning a certain total
quantity of moment of momentum was communicated to our system, and not
one particle of that total can the solar system, as a whole, squander or
alienate. No matter what be the mutual actions of the various bodies of
the system, no matter what perturbations they may undergo--what tides
may be produced, or even what mutual collisions may occur--the great law
of the conservation of moment of momentum must be obeyed. If some bodies
in the solar system be losing moment of momentum, then other bodies in
the system must be gaining, so that the total quantity shall remain
unaltered. This consideration is one of supreme importance in connection
with the tides. The distribution of moment of momentum in the system is
being continually altered by the tides; but, however the tides may ebb
or flow, the total moment of momentum can never alter so long as
influences external to the system are absent.

We must here point out the contrast between the endowment of our system
with energy and with moment of momentum. The mutual actions of our
system, in so far as they produce heat, tend to squander the energy, a
considerable part of which can be thus dissipated and lost; but the
mutual actions have no power of dissipating the moment of momentum.

The total moment of momentum of the solar system being taken to be 100,
this is at present distributed as follows:--

Orbital moment of momentum of Jupiter 60
Orbital moment of momentum of Saturn 24
Orbital moment of momentum of Uranus 6
Orbital moment