out the pliant materials of which he seems to be
formed.

Jupiter is not, so far as we can see, a solid body. This is an important
circumstance; and therefore it will be necessary to discuss the matter
at some little length, as we here perceive a wide contrast between this
great planet and the other planets which have previously occupied our
attention. From the measurements already given it is easy to calculate
the bulk or the volume of Jupiter. It will be found that this planet is
about 1,300 times as large as the earth; in other words, it would take
1,300 globes, each as large as our earth, all rolled into one, to form a
single globe as large as Jupiter.

If the materials of which Jupiter is composed were of a nature analogous
to the materials of the earth, we might expect that the weight of the
planet would exceed the weight of the earth in something like the
proportion of their volumes. This is the matter now proposed to be
brought to trial. Here we may at once be met with the query, as to how
we are to find the weight of Jupiter. It is not even an easy matter to
weigh the earth on which we stand. How, then, can we weigh a mighty
planet vastly larger than the earth, and distant from us by some
hundreds of millions of miles? Truly, this is a bold problem. Yet the
intellectual resources of man have proved sufficient to achieve this
feat of celestial engineering. They are not, it is true, actually able
to make the ponderous weighing scales in which the great planet is to be
cast, but they are able to divert to this purpose certain natural
phenomena which yield the information that is required.

Such investigations are based on the principle of universal gravitation.
The mass of Jupiter attracts other masses in the solar system. The
efficiency of that attraction is more particularly shown on the bodies
which are near the planet. In virtue of this attraction certain
movements are performed by those bodies. We can observe their character
with our telescopes, we can ascertain their amount, and from our
measurements we can calculate the mass of the body by which the
movements have been produced. This is the sole method which we possess
for the investigation of the masses of the planets; and though it may
be difficult in its application--not only from the observations which
are required, but also from the intricacy and the profundity of the
calculations to which those observations must be submitted--yet, in the
case of J