affinity, in the universe; and hence only one kind of life.  Looked at in its relation to the whole, life appears like a transient phenomenon of matter.  I will not say accidental; it seems inseparably bound up with the cosmic processes, but, I may say, fugitive, superficial, circumscribed.  Life comes and goes; it penetrates but a little way into the earth; it is confined to a certain range of temperature.  Beyond a certain degree of cold, on the one hand, it does not appear; and beyond a certain degree of heat, on the other, it is cut off.  Without water or moisture, it ceases; and without air, it is not.  It has evidently disappeared from the moon, and probably from the inferior planets, and it is doubtful if it has yet appeared on any of the superior planets, save Mars.

Life comes to matter as the flowers come in the spring,—­when the time is ripe for it,—­and it disappears when the time is over-ripe.  Man appears in due course and has his little day upon the earth, but that day must as surely come to an end.  Yet can we conceive of the end of the physical order? the end of gravity? or of cohesion?  The air may disappear, the water may disappear, combustion may cease; but oxygen, hydrogen, nitrogen, and carbon will continue somewhere.

V

Science is the redeemer of the physical world.  It opens our eyes to its true inwardness, and purges it of the coarse and brutal qualities with which, in our practical lives, it is associated.  It has its inner world of activities and possibilities of which our senses give us no hint.  This inner world of molecules and atoms and electrons, thrilled and vibrating with energy, the infinitely little, the almost infinitely rapid, in the bosom of the infinitely vast and distant and automatic—­what a revelation it all is! what a glimpse into “Nature’s infinite book of secrecy”!

Our senses reveal to us but one kind of motion—­mass motion—­the change of place of visible bodies.  But there is another motion in all matter which our senses do not reveal to us as motion—­molecular vibration, or the thrill of the atoms.  At the heart of the most massive rock this whirl of the atoms or corpuscles is going on.  If our ears were fine enough to hear it, probably every rock and granite monument would sing, as did Memnon, when the sun shone upon it.  This molecular vibration is revealed to us as heat, light, sound, electricity.  Heat is only a mode of this invisible motion of the particles of matter.  Mass motion is quickly converted into this molecular motion when two bodies strike each other.  May not life itself be the outcome of a peculiar whirl of the ultimate atoms of matter?