science attempts to supplement,
but scarcely ventures to supersede it.

Thought has, in many directions, been profoundly modified by Mayer's and
Joule's discovery, in 1842, of the equivalence between heat and motion.
Its corollary was the grand idea of the "conservation of energy," now
one of the cardinal principles of science. This means that, under the
ordinary circumstances of observation, the old maxim _ex nihilo nihil
fit_ applies to force as well as to matter. The supplies of heat, light,
electricity, must be kept up, or the stream will cease to flow. The
question of the maintenance of the sun's heat was thus inevitably
raised; and with the question of maintenance that of origin is
indissolubly connected.

Dr. Julius Robert Mayer, a physician residing at Heilbronn, was the
first to apply the new light to the investigation of what Sir John
Herschel had termed the "great secret." He showed that if the sun were a
body either simply cooling or in a state of combustion, it must long
since have "gone out." Had an equal mass of coal been set alight four or
five centuries after the building of the Pyramid of Cheops, and kept
burning at such a rate as to supply solar light and heat during the
interim, only a few cinders would now remain in lieu of our undiminished
glorious orb. Mayer looked round for an alternative. He found it in the
"meteoric hypothesis" of solar conservation.[1153] The importance in the
economy of our system of the bodies known as falling stars was then (in
1848) beginning to be recognised. It was known that they revolved in
countless swarms round the sun; that the earth daily encountered
millions of them; and it was surmised that the cone of the zodiacal
light represented their visible condensation towards the attractive
centre. From the zodiacal light, then, Mayer derived the store needed
for supporting the sun's radiations. He proved that, by the stoppage of
their motion through falling into the sun, bodies would evolve from
4,600 to 9,200 times as much heat (according to their ultimate velocity)
as would result from the burning of equal masses of coal, their
precipitation upon the sun's surface being brought about by the
resisting medium observed to affect the revolutions of Encke's comet.
There was, however, a difficulty. The quantity of matter needed to keep,
by the sacrifice of its movement, the hearth of our system warm and
bright would be very considerable. Mayer's lowest estimate put it at
9