22 HEAT. 



The pendulum approaching the vertical plane (the position of equilibrium for 

 a resting pendulum) from the highest point of its excursion possesses in this 

 position the greatest amount of kinetic energy ; and ascending to the highest point 

 of its excursion on the other side it attains, at the expense of the progressively 

 diminishing movement and thereby also the kinetic energy, again gradually the 

 maximum of potential energy. 



Heat : Its Relation to Kinetic Energy and to Potential Energy. If 



a leaden weight be thrown from the summit of a tower to the earth 

 and there encounter an unyielding surface, its movement in mass 

 will come to rest, but the kinetic energy, which to the eye appears 

 dissipated, is transformed into an actively vibratory movement of the 

 atoms. On striking the ground heat is generated, the amount of which 

 is proportionate to the kinetic energy that is transformed by the impact. 

 At the moment of contact on the part of the falling weight the atoms 

 are set into vibration by the concussion. They impinge upon one 

 another and then rebound in consequence of the potential energy that 

 tends to prevent their immediate apposition; they separate to a maxi- 

 mum degree in so far as the power of attraction of the ponderable 

 atoms permits and they oscillate to and fro in this manner. All atoms 

 oscillate like a pendulum until their movement is transmitted to all 

 the surrounding ether- atoms, that is, until the heat of the heated mass 

 is radiated. Heat is a vibratory movement of the atoms. As the 

 amount of heat generated is proportionate to the kinetic energy that 

 is transformed by the impact, it must be possible to find an adequate 

 measure for both forms of force. 



The heat-unit (calory), that is, the energy that raises the tempera- 

 ture of i gram of water i C., serves as the measure of the amount 

 of heat. This heat-unit corresponds to 425.5 grammeters; that is, the 

 same amount of energy that raises the temperature of i gram of water 

 i C. is capable of raising a weight of 425.5 grams to a height of i meter; 

 or, a weight of 425.5 grams falling from the height of i meter would 

 in its impact generate so much heat as would raise the temperature of 

 i gram of water i C. The mechanical equivalent of the heat-unit is 

 therefore 425.5 grammeters. 



It is evident that from the impact of masses in motion an amount of heat of 

 immeasurable degree may be generated. If this statement be applied to the 

 planets, their impact would result in the production of an amount of heat greater 

 than could be generated by any form of earthly combustion. If the earth were 

 suddenly checked in its course and if through the force of gravitation it plunged 

 into the sun [in the course of which it would eventually have acquired a terminal 

 velocity of 630.7 kilometers in a second] an amount of heat would be generated in 

 consequence of the collision equivalent to that produced by the combustion of 

 more than 5000 equally heavy masses of pure carbon. In this manner the dem- 

 onstration can be made scientifically, that even the sun's heat may have been 

 produced by the impact of cold matter. If the cold matter of the universe were 

 thrown into space, and there left to the attraction of its particles, the impact of 

 these masses would eventually extinguish the light of the stars. In the same way 

 numerous cosmic bodies still collide in space, and innumerable meteors constantly 

 plunge into the sun (from 9400 to 188,000 billions of kilos in each minute). 

 Thus, the action of the force of gravitation is in fact perhaps the exclusive 

 origin of all heat. The following is an instance of the transformation of kinetic 

 energy into heat: The smith makes a piece of iron hot by hammering. The fol- 

 lowing is an instance of the transformation of heat into kinetic energy: The hot 

 steam of the steam-engine causes the piston to rise. The following is an illustra- 

 tion of the transformation of potential energy into heat : The unwinding of a coiled 

 metallic spring, rubbing upon a rough surface, produces heat by friction. Exam- 



