out its energy and fritter it off into the
space about it, ultimately running completely down, as surely as any
human-made machine whose power is not from time to time restored. If,
then, it shall come to pass in some future age that the sun's rays
fail us, the temperature of the globe must gradually sink towards the
absolute zero. That is to say, the molecules of gas which now fly about
at such inconceivable speed must drop helpless to the earth; liquids
must in turn become solids; and solids themselves, their molecular
quivers utterly stilled, may perhaps take on properties the nature of
which we cannot surmise.

Yet even then, according to the current hypothesis, the heatless
molecule will still be a thing instinct with life. Its vortex whirl will
still go on, uninfluenced by the dying-out of those subordinate quivers
that produced the transitory effect which we call temperature. For those
transitory thrills, though determining the physical state of matter as
measured by our crude organs of sense, were no more than non-essential
incidents; but the vortex whirl is the essence of matter itself. Some
estimates as to the exact character of this intramolecular motion,
together with recent theories as to the actual structure of the
molecule, will claim our attention in a later volume. We shall also
have occasion in another connection to make fuller inquiry as to the
phenomena of low temperature.

APPENDIX

REFERENCE-LIST

CHAPTER I

THE SUCCESSORS OF NEWTON IN ASTRONOMY (1) (p. 10). An Account of Several
Extraordinary Meteors or Lights in the Sky, by Dr. Edmund Halley. Phil.
Trans. of Royal Society of London, vol. XXIX, pp. 159-162. Read before
the Royal Society in the autumn of 1714. (2) (p. 13). Phil. Trans. of
Royal Society of London for 1748, vol. XLV., pp. 8, 9. From A Letter to
the Right Honorable George, Earl of Macclesfield, concerning an Apparent
Motion observed in some of the Fixed Stars, by James Bradley, D.D.,
Astronomer Royal and F.R.S.

CHAPTER II

THE PROGRESS OF MODERN ASTRONOMY

(1) (p. 25). William Herschel, Phil. Trans. for 1783, vol. LXXIII. (2)
(p. 30). Kant's Cosmogony, ed. and trans. by W. Hartie, D.D., Glasgow,
900, pp. 74-81. (3) (p. 39). Exposition du systeme du monde (included in
oeuvres Completes), by M. le Marquis de Laplace, vol. VI., p. 498. (4)
(p. 48). From The Scientific Papers of J. Clerk-Maxwell, edited by W.
D. Nevin, M.A. (2 vols.),