is called "energy of position," that is, the outer parts of our
primitive nebula had a very long distance through which to travel
towards one another in the slow process of concentration; and
this distance was the measure of the quantity of work possible to
our system. As the particles of our nebula drew nearer and nearer
together, the energy of position continually lost reappeared
continually as heat, of which the greater part was radiated off,
but of which a certain amount was retained. All the gigantic
amount of work achieved in the geologic development of our earth
and its companion planets, and in the development of life
wherever life may exist in our system, has been the product of
this retained heat. At the present day the same wasteful process
is going on. Each moment the sun's particles are losing energy of
position as they draw closer and closer together, and the heat
into which this lost energy is metamorphosed is poured out most
prodigally in every direction. Let us consider for a moment how
little of it gets used in our system. The earth's orbit is a
nearly circular figure more than five hundred million miles in
circumference, while only eight thousand miles of this path are
at any one time occupied by the earth's mass. Through these eight
thousand miles the sun's radiated energy is doing work, but
through the remainder of the five hundred million it is idle and
wasted. But the case is far more striking when we reflect that it
is not in the plane of the earth's orbit only that the sun's
radiance is being poured out. It is not an affair of a circle,
but of a sphere. In order to utilize all the solar rays, we
should need to have an immense number of earths arranged so as to
touch each other, forming a hollow sphere around the sun, with
the present radius of the earth's orbit. We may well believe
Professor Tyndall, therefore, when he tells us that all the solar