242 THOUGHTS ON THE NATURE AND ORIGIN OF FORCE. 



effect. So if a pound of gunpowder will impel a cannon-ball with a 

 given velocity, it will require four pounds of powder to double that 

 velocity. The conservatiou of force, however, is maintained in the fact 

 that the penetrating power of the cannon-ball is directly proportional 

 to the energy expended in its propulsion ; or, in other words, to the square 

 of its velocity. Or, to express the distinction in the established formula- 

 while in X V represents the quantity of motion in a moving body, m x r 

 represents its quantity of fo7xe. 



Secondly, in regard to static force : Every one who has ever attempted 

 to hold aloft a heavy weight as motionless as possible will have had a 

 realizing sense of the expenditure of energy required, not to produce^ 

 but to prevent motion. The Suspension Bridge at Niagara, safely uphold- 

 ing its thousands of tons of loaded cars and human freight over the 

 frightful chasm beneath, may be cited as one among an infinite number 

 of examples of statical force, or of fou-er in repose. 



The avalanche, hurtling down the mountain side with destructive vio- 

 lence, overwhelming a village and its inhabitants, is but expending a 

 force stored up a year or years before, by the sun, when it lifted the 

 mass, molecule by molecule, to its position of latent or potential energy. 



Every pound of coal possesses a static or potential force of ten million 

 ''foot-pounds." That is to say, the power expended by the sun in rais- 

 ing the pound of coal from its low estate of chemical combination, or a 

 satisfied affinity, to the higher plane of isolation and capacity for chem- 

 ical reunion, was a power capable of lifting one thousand pounds of 

 water to the height of ten thousand feet. And, conversely, the pound 

 of coal thus chemically raised has itself received the power of mechan- 

 ically lifting that immense weight to tliat enormous height. 



It must be borne in mind, however, that when the sun actually does 

 lift a thousand pounds of water to the height mentioned, it does not 

 raise it bodily as water; it performs the vast additional labor of tearing 

 asunder the entire mass, molecule by molecule, in opposition to the 

 statical force of an intense cohesive attraction : a work of more than 

 ten thousand "foot-pounds;" an expenditure of energy greater than 

 that required to grind the same weight of ice (one thousand pounds) to 

 the most impalpable powder. Deducting, therefore, this expenditure 

 (a little over ten thousand " foot-pounds") we should find that the i^ound 

 of coal represents, in a static form, an invested power eipiivalent to 

 the lifting of one thousand pounds of water a little more than one foot, 

 in addition to the task of evaporating the whole amount.* 



Matter in motion being thus merely a vehicle of force, it follows that 

 wherever dynamic or kinetic energy is transformed into potential energy, 

 (as in pumping up water into an elevated reservoir,) there motion is to 

 this extent destroyed; wherever potential or static energy is trans- 

 formed into dynamic, (as in the discharge of aloaded pistol,) there motion is 



* This of course does not include auy actual heating of the water. One pound of 

 coal will raise tbirteeu thousand pounds of water 1"^ ; which is equivaleut to only sev- 

 enty-two pounds of ice-cold water (32°) raised to the boiling point, (212°.) 



