284 FRAGMENTS OF SCIENCE. 



enormous force of the collision. The burning of charcoal 

 in oxygen is an old experiment, but it has now a signifi- 

 cance beyond what it used to have; we now regard the act 

 of combination on the part of the atoms of oxygen and 

 coal as we regard the clashing of a falling weight against 

 the earth. The heat produced in both cases is referable to 

 a common cause. A diamond, which burns in oxygen as a 

 star of white light, glows and burns in consequence of the 

 falling of the atoms of oxygen against it. And could we 

 measure the velocity of the atoms when they clash, and 

 could we find their number and weights, multiplying the 

 weight of each atom by the square of its velocity, and add- 

 ing all together, we should get a number representing the 

 exact amount of heat developed by the union of the oxygen 

 and carbon. 



Thus far we have regarded the heat developed by the 

 clashing of sensible masses and of atoms. Work is ex- 

 pended in giving motion to these atoms or masses, and heat 

 is developed. But we reverse this process daily, and by 

 the expenditure of heat execute work. We can raise a 

 weight by heat; and in this agent we possess an enormous 

 store of mechanical power. A pound of coal produces by 

 its combination with oxygen an amount of heat which, if 

 mechanically applied, would suffice to raise a weight of 

 100 Ibs. to a height of 20 miles above the earth's surface. 

 Conversely, 100 Ibs. falling from a height of 20 miles, and 

 striking against the earth, would generate an amount of 

 heat equal to that developed by the combustion of a pound 

 of coal. Wherever work is done by heat, heat disappears. 

 A gun which fires a ball is less heated than one which fires 

 blank cartridge. The quantity of heat communicated to 

 the boiler of a working stearn-engine is greater than that 

 which could be obtained from the re condensation of the 

 steam, after it had done its work; and the amount of work 

 performed is the exact equivalent of the amount of heat 

 lost. Mr. Smyth informed us in his interesting discourse, 

 that we dig annually 84 millions of tons of coal from our 

 pits. The amount of mechanical force represented by this 

 quantity of coal seems perfectly fabulous. The combustion 

 of a single pound of coal, supposing it to take place in a 

 minute, would be equivalent to the work of 300 horses; 

 and if we suppose 108 millions of horses working day and 

 night with unimpaired strength, for a year, their united 



