372 FEAGMENTS 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 velo- 

 city would be small for a rifle bullet ; multiplying J-ths 

 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. 1 



From the motion of sensible masses, by gravity and 

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

 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 electric 

 light was suddenly generated ; the instant the concen- 

 trated 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 pro- 

 duced showing the enormous force of the collision. 

 The burning of charcoal in oxygen is an old experi- 

 ment, 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- 



1 Eight years subsequently this surmise was proved correct. 

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

 case of bullete impinging on bones. 



