373 
i88o.] The Origin of Falling Motion. 
in response to gravitation. These two energies are exadtly 
balanced ; neither can accumulate at the expense of the 
other, and they result in a circular orbit. But there is a 
third motion, a vertical vibration in the line of the radius, 
a vibration of some three millions of miles in extent, each 
phase of which occupies six months. This vibratory move- 
ment has its full effedb upon the resultant motion of the 
earth, changing its orbit from a circle into an ellipse. 
But the vertical vibration is resisted by gravitation in its 
outward phase, and aided in its inward phase. The result 
is that a portion of the motive energy of the earth is con- 
sumed, by the resistance of solar gravitation, during its 
outward movement. This lost mass motion must fall back 
into the earth and become a vibration of particles, consti- 
tuting an increase of temperature. Its inward movement 
is, on the contrary, aided by gravitation. The mass motion 
increases at the expense of the temperature energy. 
The loss of mass motion in the earth, from this cause, 
between perihelion and aphelion, is about ij miles, or 
6600 feet, per second. It will consequently not be difficult 
to obtain an idea of the amount of variation in temperature 
from this cause. For we know that a mass of water, when 
arrested after a fall of 772 feet, gains i° F. in temperature 
from a conversion of its mass motion into heat vibration. 
Now a fall of 772 feet yields a final velocity of about 220 feet 
per second. If the loss of this velocity yields water a tem- 
perature of i°, the loss of 6600 feet per second of velocity 
by the earth should yield it an increased temperature of 
30° F., supposing its mean specific heat to equal that of 
water. If the specific heat equalled that of iron the in- 
creased temperature would be about 270°, and if equal to 
mercury it would be 900°. 
We have here a very marked result, but one that is not 
strikingly evident, from the fadt that this lost motion is not 
an instantaneous arrest, but a gradual arrest extending over 
six months. The true result, then, is daily increase in 
temperature, for every particle of water in the earth of one- 
sixth of a degree, of i£° for every particle of iron, of 
5 per cent for every particle of mercury, and a like result for 
every other substance in accordance with its specific heat. 
During the return movement of the earth, from aphelion to 
perihelion, the opposite effe<ft results. Its mass motion in- 
creases, at the expense of its temperature, to an equal 
degree. 
This variation in temperature cannot have any very evi- 
dent effect at the surface of the earth, where it is lost in 
