374 THE POPULAR SCIENCE MONTHLY. 



phenomena of Nature are to be regarded merely as varieties of motion, 

 one guiding principle of which is conservation of energy. This being 

 an established fact in science, it fortifies us in our position of reasoning 

 downward in the direction of primary causes. By conservation of ener- 

 gy we are to understand that, while matter exists throughout the uni- 

 verse in definite quantity, there is also existing, as an attribute of mat- 

 ter, a definite amount of energy or force ; and just so sure as matter is 

 indestructible and ^^?^changeable, just so sure is force or energy inde- 

 structible and inter ch.a,ngeah\Q. That is, matter and force are both 

 indestructible, but force or energy (synonymous terms) is convertible 

 into the several modes of force. The attributes of matter are attrac- 

 tion of gravitation, attraction of cohesion, and chemical affinity. At- 

 traction of gravitation is a force exerted upon each and every atom 

 of matter throughout the universe, with a never-ending geometric ratio, 

 varying directly as the mass and inversely as the square of the distance. 

 The force known as chemical affinity binds the integral particles of 

 compounds in an embrace many millions of times stronger than that of 

 gravitation, but, like cohesive attraction, is incompetent to exert its 

 power beyond very short distances, such as those measured by the 

 limits of the molecule. 



The correlation of physical forces has for its domain the interchange- 

 ableness and universality of the forces of Nature. It is competent to 

 solve the dynamical problems of vital and physical phenomena, demand- 

 ing from every antecedent its consequent, and exacting from every 

 consequent an equivalency of antecedent. All sound experience of 

 whatever kind justifies this affirmation. These views compel the idea 

 of the universality of motion, and that force is the eternal causation of 

 each and every phenomenon, and that the existing relations between 

 matter and force remain constant throughout the universe. The same 

 forces that whirl suns and planets in a restless march through shoreless 

 space measure the phenomena of the moments of life. 



The different consequents of molecular motion are sound, light, 

 heat, etc., the antecedents of them all being some mode of motion. 

 By the term " mode of motion " is meant the manner in which ener- 

 gies are made sensible to our understanding. Thus, the terms heat, 

 light, etc., are but familiar ones by which we express the various modes 

 in which force is exhibited to our senses in its action upon matter. 

 Conservation of energy was denominated by Faraday as " the highest 

 law in physical science which our faculties permit us to perceive." Its 

 unfoldings mark an intellectual epoch which divides the old from the 

 new. It teaches of the unity of the universe ; it tells us how the 

 sun's rays constitute the mighty energies of daily life and action upon 

 every hand, warming, illuminating, and vivifying the surface of the globe. 

 As an illustration of this interchangeableness of force : suppose two 

 files of men to be arranged in proper order, between which we roll a 

 cannon-ball with a certain initial velocity. This ball runs the gantlet 



