1880.J The Origin of Falling Motion . 371 
momentary falls are each obliterated by a reverse impaCt, 
and cannot be added together, constituting an increasing 
energy of fall. Only when the resistance is removed, and 
the particles are no longer driven back by impaCt, does the 
falling energy manifest itself in a downward movement of 
the mass. . 
Thus, when a body falls, part of its heat motion has been 
transformed, and has become motion of the mass as a whole. 
The generalised motion of heat has become partly special- 
ised into motion of the mass. This is readily transformable 
again into heat; but it can only be so transformed by re- 
sistance. It is persistent as mass motion until some resisting 
energy overcomes it, when it again becomes heat. 
And from this faCt two conclusions necessarily arise. The 
first is, that a body whose mass motion is resisted must dis- 
play an increase of temperature. The confoimity in the 
motion of the particles is broken ; they again move indivi- 
dually instead of collectively. Temperature effects appear 
in consequence. 
The other conclusion is, that a body yielding to gravita- 
tion, in increasing its mass motion, must decrease in tem- 
perature. Its temperature is being converted into another 
form of force, and cannot continue to display its usual 
effects. The body grows colder in every direction except 
that of its mass motion, the movements of the particles 
being specialised in this direction, and their impacting force 
partly decreased in all other directions. 
The heat thus lost, as heat, is probably regained from the 
radiations of the matter through which the body moves, so 
that its sum of forces is increased in consequence of a spe- 
cial transformation of a portion of them. 
Where the motion of the body is decreased or increased 
by gravitation, without radiation of heat from other sources, 
certain interesting and perhaps important effects must ensue. 
If a mass be driven upward against gravitation its particles 
must continue to fall. The downstroke of their vertical 
component of motion, as caused by gravitation, is constantly 
more vigorous than the upstroke. I he fall of .the body is 
simply masked by its upward motion, and accumulates in 
the same manner as if the mass was descending. I hus the 
upward motion is more and more rapidly obliterated, and 
soon ceases to exist, the mass becoming momentarily at 
rest. What has become of the mass motion ? Evidently 
there has been a simple change in the character of the mo- 
tion of the particles. Instead of moving upwards more 
rapidly than they descended, they now move upward and 
