OX FORCE. 283 
double your velocity, other things remaining equal, and 
you quadruple your amount of heat. Here then we have 
common mechanical motion destroyed and heat produced. 
When a violin bow is drawn across a string, the sound 
produced is due to motion imparted to the air, and to 
produce that motion muscular force has been expended. 
We may here correctly say, that the mechanical force of 
the a*rm is converted into music. In a similar way we say 
that the arrested motion of our descending weight, or of 
the cannon ball, is converted into heat. The mode of 
motion changes, but motion still continues; the motion of 
the mass is converted into a motion of the atoms of the 
mass; and these small motions, communicated to the 
nerves, produce the sensation we call heat. 
AVe know the amount of heat which a given amount of 
mechanical force can develop. Our lead ball, for ex- 
ample, 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 82 feet a second, and forty times this velocity would be 
small for a rifle bullet; multiplying three-fifths 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 toward 
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 sud- 
denly generated; the instant the concentrated light fell 
upon the balloon, the gases within it exploded, hydro- 
chloric acid being the result. Here the atoms virtually fell 
together, the amount of heat produced showing the 
* 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. 
