372 FKAGMENTS OF SCIENCE. 



We know the amount of heat which a given amount 

 of mechanical force can develope. Our lead ball, for 

 example, in falling to the earth generated a quantity of 

 heat sufficient to raise its own temperature three-fifths 

 of a Fahrenheit degree. It reached the earth with a 

 velocity of 32 feet a second, and forty times this veloc- 

 ity would be small for a rifle bullet; multiplying -fths 

 by the square of 40, we find that the amount of heat 

 developed by collision with the target would, if wholly 

 concentrated in the lead, raise its temperature 960 

 degrees. This would be more than sufficient to fuse 

 the lead. In reality, however, the heat developed is 

 divided between the lead and the body against which 

 it strikes; nevertheless, it would be worth while to pay 

 attention to this point, and to ascertain whether rifle 

 bullets do not, under some circumstances, show signs 

 of fusion.* 



From the motion of sensible masses, by gravity and 

 other means, we now pass to the motion of atoms to- 

 wards each other by chemical affinity. A collodion 

 balloon filled with a mixture of chlorine and hydrogen 

 being hung in the focus of a parabolic mirror, in the 

 focus of a second mirror 20 feet distant a strong elec- 

 tric light was suddenly generated; the instant the 

 concentrated light fell upon the balloon, the gases 

 within it exploded, hydrochloric acid being the result. 

 Here the atoms virtually fell together, the amount of 

 heat produced showing the enormous force of the col- 

 lision. The burning of charcoal in oxygen is an old 

 experiment, but it has now a significance 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 re- 



* Eight years subsequently this surmise was proved correct. 

 In the Franco-German War signs of fusion were observed in the 

 case of bullets impinging on bones. 



