1862.] on Force. 531 



throughout its entire range. Place a body at such a distance from the 

 earth that the attraction of the earth is barely sensible, and let it fall 

 to the earth from this distance. It would reach the earth with a final 

 velocity of 36,747 feet in a second ; and on collision with the earth the 

 body would generate about twice the amount of heat generated by the 

 combustion of an equal weight of coal. We have stated that by falling 

 through a space of 16 feet our lead bullet would be heated three-fifths 

 of a degree ; but a body falling from an infinite distance has already 

 used up 1,299,999 parts out of 1,300,000 of the earth's pulling power, 

 when it has arrived within 16 feet of the surface ; on this space only 

 Yj^^^-g^^ths of the whole force is exerted. 



Let us now turn our thoughts for a moment from the earth towards 

 the Sim. The researches of Sir John Herschel and M. Pouillet have 

 informed us of the annual expenditure of the sun as regards heat ; and 

 by an easy calculation we ascertain the precise amount of the expendi- 

 ture which falls r,o the share of our planet. Out of 2300 million parts 

 of light and heat the earth receives one. The whole heat emitted by 

 the sun in a minute would be competent to boil 12,000 millions of cubic 

 miles of ice-cold water. How is this enormous loss made good? 

 Whence is the sun's heat derived, and by what means is it maintained ? 

 No combustion, no chemical affinity with which we are acquainted 

 would be competent to produce the temperature of the sun's surface. 

 Besides, were the sun a burning body merely, its light and heat would 

 assuredly speedily come to an end. Supposing it to be a solid globe of 

 coal, its combustion would only cover 4600 years of expenditure. In 

 this short time it would burn itself out. What agency then can pro- 

 duce the temperature and maintain the outlay ? We have already re- 

 garded the case of a body falling from a great distance towards the 

 earth, and found that the heat generated by its collision would be twice 

 that produced by the combustion of an equal weight of coal. How much 

 greater must be the heat developed by a body falling towards the sun ! 

 The maximum velocity with which a body can strike the earth is about 

 7 miles in a second ; the maximum velocity with which it can strike 

 the sun is 390 miles in a second. And as the heat developed by the 

 collision is proportional to the square of the velocity destroyed, an 

 asteroid falling into the sun with the above velocity would generate 

 about 10,000 times the quantity of heat generated by the combustion of 

 an asteroid of coal of the same weight. Have we any reason to believe 

 that such bodies exist in space, and that they may be raining down upon 

 the sun ? The meteorites flashing through the air are small planetary 

 bodies, drawn by the earth's attraction, and entering our atmosphere 

 with planetary velocity. By friction against the air they are raised 

 to incondescence and caused to emit light and heat. At certain seasons 

 of the year they shower down upon us in great numbers. In BostoD 

 240,000 of them were observed in nine hours. There is no reason to 

 suppose that the planetary system is limited to " vast masses of 

 enormous weight;" tliere is eveiy reason to believe that space is 

 stocked with smaller masses, which obey the same laws as the large 



