322 Dynamic Theory. 



ing motion from one shaft to another, we should find ourselves becom- 

 ing charged with electricity, and we could pass this electricity off in the 

 shape of a spark from the end of a finger to another object. If that 

 other object should happen to be the cheek or nose of a bystander, a 

 further molecular effect would be observed in a slight sting in the re- 

 ceiving cheek and possibly in the delivering finger. Thus we trace the 

 energy of the falling water through various forms of motion, which 

 forms depend on the forms and adjustments of the various movable 

 pieces of mechanism with which the energy comes into contact. If we 

 go back to inquire how the water came to be in a position to give off 

 this energy in the first place, we shall find the energy to begin with the 

 sun's rays, which, acting upon the water of a tropical sea, sets up a 

 molecular movement of the water, which results in evaporation. The 

 same heat rays acting upon the air expands it making it lighter. By 

 the simple laws of equilibrium colder and heavier air glides under this 

 light air forcing it upward together with the products of the evapora- 

 tion, which are thus raised,, and then by the winds carried over the land 

 till they are finally cooled, condensed and precipitated in rain. In this 

 case molecular energy, set up in two unlike bodies by the same original 

 force from the sun, but acting in different ways on account of the dif- 

 ference of the physical forms of the mediums acted upon, ends by be- 

 coming molar or mechanical energy. Any other form of mechanical 

 energy, as steam power, horse power, or man power, may be traced 

 back to molecular motion in the burning of fuel, or the consumption of 

 food in the first place, and to the solar radiation in the production of 

 vegetation at last. In short, the most of the forms of energy that we 

 find on earth are traceable to the solar radiations, and all are, in fact, 

 at bottom only one. The forms taken are transient and temporary, but 

 the aggregate amount is constant. 



As mentioned above, some of the names of forms of energy are only 

 the names of phenomena. Such are heat, light and sound. These are 

 only sensations of ours ; that is, pieces of our minds. We feel the heat, 

 see the light and hear the sound. Most other animals do the same, and 

 most plants are affected by heat and light in a way which forms the 

 basis of our senses. Indeed, even minerals suffer the effects of what 

 we, in a loose way, call heat and light, but at any rate these terms 

 properly apply, only, to a class of motions .called mental, and when 

 molecular vibrations do not end by giving rise to this class of motions, 

 these terms are inaccurate and are used only because convenient. A 

 body may be in a condition of violent molecular vibration, but the word 

 hot does not express this, but only our sensation of it. The same is 

 true of light and sound. 



The motions, as they happen outside of ourselves, are, in the case of 



