SECT. XXVII. DYNAMIC POWER IN NATURE. 279 



the steam engine for example is exactly proportional to the con- 

 sumption of heat, nor more nor less ; if we could produce a greater 

 quantity than its equivalent we should have perpetual motion, 

 which is impossible. Mechanical engines generate no force. We 

 cannot create force ; we can only avail ourselves of the inexhaust- 

 ible stores of nature, the lightning, fire, water, wind, chemical 

 action, &c. The quantity of mechanical power in nature is ever 

 the same ; it is never increased, it is never diminished, through- 

 out the whole circuit of natural powers. The conservation of force 

 is as permanent and unchangeable as matter. It may be dormant 

 for a time, but it ever exists. We are unconscious of the enor- 

 mous dynamic power that is either active or latent throughout 

 the globe, because we do not attend to it. By the ebb and flow 

 of the tide alone a power is exerted by which 25,000 cubic miles 

 of water is moved over a quarter of the globe every twelve hours ; 

 and Professor W. Thomson has computed, by means of Pouillet's 

 data of solar radiation and Mr. Joule's mechanical equivalent of 

 heat, that the mechanical value of the whole energ}^ active and 

 potential of the disturbances kept up in the ethereal medium by 

 the vibrations of the solar light within a cubic mile of our atmos- 

 phere is equal to 12,050 times the unit of mechanical force, that 

 is to say, 12,050 times the force that would raise a pound of 

 matter to the height of one foot, whence some idea may be formed 

 of the vast amount of force exerted by the sun's light within the 

 limits of the whole terrestrial atmosphere. (N. 223.) 



The dynamic energy of the undulations of the solar light gives 

 the leaves of plants the power of decomposing carbonic acid, and 

 of separating the particles of carbon and hydrogen from the 

 oxygen for which they have so strong an affinity. In this operation 

 the undulations of the sunbeam are extinguished as light and heat, 

 and Professor W. Thomson has proved that the quantity of these 

 undulations thus extinguished is precisely equal to the potential 

 or quiescent energy thus created, and that precisely that very 

 quantity of light and heat is restored when the plants are burned, 

 whatever state they may be in ; and that thus, as Mr. George 

 Stephenson* has truly and beautifully observed, our coal fires 



* To this remarkable man the world is indebted for the locomotive rail- 

 way system, which is rapidly advancing the civilization of mankind. 

 Britain may well be proud of its working classes, which can produce such 

 men ; and Mr. George Stephenson is not the only one ; there are many others ; 

 but no man has ever had greater influence by his labours and discoveries on 

 human affairs. 



