ure
decreases, one after another of the chemical elements makes its
appearance, the simpler elements appearing first, and the more complex
compounds appearing last, all apparently having their origin in some
simple parent element. It appears as if the evolution of life upon the
globe had followed the same law and had waited upon the secular cooling
of the earth.

Does not a man imply a cooler planet and a greater depth and refinement
of soil than a dinosaur? Only after a certain housecleaning and
purification of the elements do higher forms appear; the vast
accumulation of Silurian limestone must have hastened the age of fishes.
The age of reptiles waited for the clearing of the air of the burden of
carbon dioxide. The age of mammals awaited the deepening and the
enrichment of the soil and the stability of the earth's crust. Who knows
upon what physical conditions of the earth's elements the brain of man
was dependent? Its highest development has certainly taken place in a
temperate climate. There can be little doubt that beyond a certain point
the running-down of the earth-temperature will result in a running-down
of life till it finally goes out. Life is confined to a very narrow
range of temperature. If we were to translate degrees into miles and
represent the temperature of the hottest stars, which is put at 30,000
degrees, by a line 30,000 miles long, then the part of the line marking
the limits of life would be approximately three hundred miles.

Life does not appear in a hard, immobile, utterly inert world, but in a
world thrilling with energy and activity, a world of ceaseless
transformations of energy, of radio-activity, of electro-magnetic
currents, of perpetual motion in its ultimate particles, a world whose
heavens are at times hung with rainbows, curtained with tremulous
shifting auroras, and veined and illumined with forked lightnings, a
world of rolling rivers and heaving seas, activity, physical and
chemical, everywhere. On such a world life appeared, bringing no new
element or force, but setting up a new activity in matter, an activity
that tends to check and control the natural tendency to the dissipation
and degradation of energy. The question is, Did it arise through some
transformation of the existing energy, or out of the preexisting
conditions, or was it supplementary to them, an addition from some
unknown source? Was it a miraculous or a natural event? We shall answer
according to our temperame