ATOMIC WORLDS AND THEIR MOTIONS. 185 



of snow ; not a sound to be heard, not a "breatli of wind stirring 

 tlie branches. 



And yet we know that all this is an illusion ! Those bright 

 points of light on the dark firmament are solar systems, whirling 

 through space two hundred times faster than a cannon-ball, and 

 under our feet the delicate snow-crystals are groups of atoms, 

 which tremble with billions of vibrations every second. 



The outer forms of the little snow-stars appear to us fixed and 

 rigid like those of the bright constellations above. But from 

 their surfaces a pale light enters our eyes, acts on the retina, and 

 excites the optic nerve — an infallible proof that there is something 

 active even in these — and we know of only one kind of activity in 

 this universe, namely, that of motion. 



The particles of which the snow-crystals are comjDosed are not 

 closely joined or cemented to each other like the stones in a wall. 

 They are perpetually acting and reacting on the bodies which 

 surround them, through the medium of an exceedingly fine sub- 

 stance which we term world-ether. It is the bearer of the move- 

 ments, the effects or modifications of which we know as light, 

 heat, electricity, chemical affinity, etc. ; it also keeps the particles 

 of the snow-crystals separate, maintains them in a state of mutual 

 equilibrium, and regulates their vibrations. These vibrations we 

 term the " mechanical cause of heat," because we are aware that 

 every increase of temperature is represented by an increase in the 

 rapidity of the vibrations. 



These minute particles, of which, as we know, all bodies con- 

 sist, are called molecules. In solids, as, for instance, the snow- 

 crystals, they are arranged in a certain fixed order, and their 

 vibration is limited to a given space. Now, let the sun shine on 

 the snow. 



The sun is a vast center of activity. From every point of its 

 surface an enoriuous number of impulses are continually acting 

 on the atoms of the surrounding ether, which are sent through 

 space in every direction, with lightning-like rapidity. The num- 

 ber of these impulses has been estimated at from four to eight 

 hundred billions per second. They give rise to a wave-like mo- 

 tion which traverses about two hundred thousand miles of space 

 per second, and requires eight minutes to reach our earth. 



If these ether-waves happen to come into contact with our 

 optic nerve, we experience the sensation of light ; if they impinge 

 upon our skin, we feel warmth ; if they strike the snow, they set 

 its molecules, as well as the ether between them, into a livelier 

 state of motion. The vibration of the molecules increases in 

 violence, and the result is an increase in temperature in the snow. 

 The particles have to move further away from each other, as their 

 vibrations require more space — we say the heat expands the 



