372 
[June, 
The Origin of Falling Motion. 
downwards with the same vigour. The special mass motion 
has fallen back into the body, and has become vibratory 
movement of its particles. It has, in fadt, become temper- 
ature, and the sum of temperature energy has increased 
through this loss of mass motion. 
If now we apply this idea to the movement of the planetary 
bodies, some interesting deductions may be made. In the 
case of a comet moving from the sun we have an exadt 
counterpart of that of a body thrown upward against gra- 
vity. The particles of the comet continue to fall towards 
the sun. These slight falls are masked in the mass motion 
of the comet, but they slowly consume this motion. They 
constantly accumulate, precisely as if the reverse motion 
did not exist. The comet is thus at once moving outward 
from the sun and falling inward to the sun, and its real 
motion is the difference between these opposite energies. 
Its mass motion is, in short, falling back into its substance, 
and becoming vibratory motion. Eventually the fall in- 
creases in vigour until it equals the outward motion of the 
mass. At this point the comet ceases to remove from the 
sun. The outward and inward movement of its particles 
have become equal ; the vertical component of their motion 
through space has become converted into a vibration about 
a fixed point in space. It has, in fadt, become heat motion. 
Thus the strange fadt displays itself of a rapidly-increasing 
temperature in the comet, as a necessary consequence of its 
movement outward from the sun. In its return to the sun 
the opposite effedt occurs. Its vibratory motion is gradually 
transformed into mass motion. Every new increment of 
mass motion thus gained is at the expense of the heat 
vibration, and the temperature necessarily decreases in con- 
sequence. 
This effedt is, of course, masked in its increased reception 
of radiant heat in approaching, and its rapid radiation into 
space while leaving the sun. It is in this like a falling body 
whose lost temperature is regained from the radiations of 
surrounding matter. 
A precisely similar effedt must occur in the case of every 
planet which has an elliptical orbit. The earth, for instance, 
after passing its perihelion point, begins to move outward 
from the sun, against gravitation ; but the fall of its parti- 
cles towards the sun at once tends to consume this outward 
movement. The earth possesses really three movements, 
from whose composition its orbital movement results. One 
of these is a movement at a tangent to the radius of its 
orbit. This is resisted by a falling motion towards the sun, 
