THOUGHTS ON THE NATURE AND ORIGIN OF FORCE. 249 



oscillatory motiou is fluallv destroyed onlj' by external and internal re- 

 sistances. In a manner somewhat analogous to this, the molecules of 

 all matter balanced between opposing attractive and repulsive ten- 

 dencies are forever ringing (so to speak) in response to continual dis- 

 turbances, though with a rapidity inconceivably greater than any 

 known as sound. Thus, when a gas-jet has its surface of contact with 

 the atmosphere smitten with a spark or blaze, the molecules of oxygen 

 and those of hydrogen and carbon rushing or falling together under the 

 impulse of an attraction known as chemical aifiuity, with a violence so 

 great as to impinge severely on their several spheres of molecular repul- 

 sion, set up a vibration whose velocity or pitch is measured by hundreds 

 of millions, in the millionth part of a second. 



When we examine other occasions of heat or molecular movement, 

 we find the actions not dissimilar. Thus, in the case of friction, it is 

 evident that the more prominent particles, pressed by either side be- 

 tween the rubbing surfaces, (not indeed by actual contact, but by 

 what is equivalent, their repulsive spheres,) momentarily forced back 

 within their repulsions and thereby compressing others, rebound with 

 a vigor proportioned to the pressure ; and thus, like a spring, continue 

 an oscillation, strengthened and accelerated by the duration of the 

 raspings. So, when a body is subjected to percussion, we see how a 

 vibration must be started, intense in i)roportion to the violence of the 

 blow, as well as to the reinforcement of repeated action. In the fire- 

 syringe, the volume of air already possessing a quantity of molecular 

 motion due to the ordinary temperature, suddenly compressed into a 

 very small space, must of necessity have the velocity of its particles 

 greatly increased, and consequently the frequency and violence of the 

 repulsive collisions correspondingly aggravated and inteusiiied. 



A similar concei^tion may be extended to the thermal, chemical, and 

 magnetic effects of electric currents, whether excited by frictional or by 

 chemical disturbance, although the precise nature of the molecular move- 

 ments is undoubtedly wrapped in great obscurity. 



As has already been indicated, all applications of animal power may 

 obviously be regarded as derived (either directly or indirectly) from the 

 static chemical power .of the vegetable substance by which the various 

 organisms and their capabilities are sustained ; and this power, in turn, 

 from the kinetic action of the sun's rays. 



Winds and ocean currents, hail-storms and rain, sliding glaciers, flow- 

 ing rivers, and falling cascades, are the direct offspring of solar heat. 

 AU our machinery, therefore, whether driven by the wind-mill or the 

 water-wheel, by horse-power or by steam — all the results of electrical 

 and electro-magnetic changes — our telegraphs, our clocks, and oiu? 

 watches, all are wound up primarily by the sun.* 



The tides, with all their lifting power, (to which the largest ocean- 



* The elder Stephenson, some fifty years ago, appears to have heen the first to form 

 the couceiition that his locomotive engines were really di'iveu by solar power. 



