NATURAL PHILOSOPHY. 113 



problem of the origin of the sun's heat. We know the connection 

 bet'.vceu the space through which a body falls, the velocity, the vis 

 r/V.v, and the generation of heat on the surface of this globe ; if 

 we again substitute for the earth the sun,- with a mass 350, O:K) 

 greater, and for a height of a few meters celestial distances, we ob- 

 tiiu a generation of heat exceeding all terrestrial measures. And 

 since we have sufficient reason to assume the actual existence of such 

 mechanical processes in the heavens, we find therein the only tenable 

 exp! ination of the origin of the heat of the sun. 



The fact that the development of heat by mechanical means on the 

 surface of our globe, is, as a rule, not so great, and cannot be so 

 great as the generation of the same agent by chemical means, as by 

 combustion, follows from the laws already discussed; and this fact 

 cannot be used as an argument against the assumption of a greater 

 development of heat by a greater expenditure of mechanical work. 

 It has been shown that the heat generated by a weight falling from a 

 higlit of 307 meters is only g-gVo P art f the neat produced by the 

 combustion of the same weight of coal ; just as small as is the amount 

 of heat developed by a weight moving with the not inconsiderable 

 velocity of 85 meters in one second. But, according to the laws of 

 mechanics, the effect is proportional to the square of the velocity ; if, 

 therefore, the weight move 100 times faster, or with a velocity of 

 8,500 meters in one second, it will produce a greater effect than the 

 combustion of an equal quantity of coal. 



It is true that so great a velocity cannot be obtained by human 

 means ; everyday experience, however, shows the development of 

 high degrees of temperature by mechanical processes. In the com- 

 mon flint and steel, the particles of steel which are struck off are 

 sufficiently heated to burn in air. A few blows directed by a skill- 

 ful blacksmith with a sledge-hammer against a piece of cold metal 

 may raise the temperature of the metal at the points of collision to 

 redness. The new crank of a steamer, whilst being polished by 

 friction, becomes red-hot, several buckets of water being required to 

 cool it down to its ordinary temperature. When a railroad train 

 passes with even less than its ordinary velocity along a very sharp 

 curve of the line, sparks are observed in consequence of the friction 

 against the rails. One of the grandest constructions for the produc- 

 tion of motion by human art is the channel in which the wood was 

 allowed to glide down from the steep and lofty sides of Mount Pila- 

 tus into the plain below. This wooden channel which was built 

 about thirty years ago by the engineer Rupp, was nine English miles 

 in length ; the largest trees were shot down it from the top to the 

 bottom of the mountain in about two minutes and a half. The mo- 

 m:'utum possessed by the trees on their escaping at their journey's end 

 from the channel was sufficiently great to bury their thicker ends in 

 the ground to the depth of from six to eight meters. To prevent 

 the wood getting too hot and taking fire, water was conducted in 

 many places into the channel. 



This stupendous mechanical process, when compared with cosmi- 

 cal processes on the sun appears infinitely small. In the latter case 

 it is the mass of the sun which attracts, and in place of the hight of 

 Mount Filatus we have distances of 100,000 and more miles ; the 



