4: 
THE GEOLOGIST. 
alteration from remarkable former conditions of our planet. Let us 
glancingly turn our eyes now in the same direction. If the earth's 
orbital velocity and her rotation round her axis are due to some 
originating impulse, such as projectile force would be to a cannon 
ball, then the orbital velocity and the rotatory motion must have 
been higher in the early ages of our planet than at present, because 
if there be any friction opposed to motion in space that friction is an 
antagonistic power, that, no matter how slowly, would bring down 
and ultimately cancel the amount of the initial velocity, and reduce 
the object to a state of rest. If we consider the effects of a higher 
orbital velocity, we shall find it would give rise probably to a larger 
extent of orbit, and also to a higher rotatory motion. Now the 
higher rotatory motion, although it would give no more sunshine 
to the earth, would so far counteract the effects of night-radiation 
into space as that if the revolution were twice as quick, the effect 
of night-radiation would possibly not be half what it is, because 
the radiation being at a given rate for a given time, it could only 
attain half the diminution of temperature in half the time, and 
we know that the more intense the cold the more vegetation is 
checTced. It might therefore happen that half our present inten- 
sity, never exceeded, might never bring vegetation to a standstill, 
and there might be a perpetual growing vegetation through both 
winter and summer under such favourable conditions. If the orbit 
were increased, these favourable conditions might, it may be seen at 
the first glance, be counteracted by the greater remoteness from the 
sun ; but we have yet to learn that the nearer the sun the hotter 
would be our planet's general climate, or the further away greater in 
proportion the diminution of light. . Is light dependent on the den- 
sity of our atmosphere, and does it travel on as simple motion in the 
ethereal realms beyond our atmosphere ? Is it the friction of waves 
of motion through our air that gives to light its luminosity? The 
sunlight falling on Neptune must be powerful, for the reflected beams 
from that far distant planet to reach us as definitely as they do in 
our powerful telescopes F And I do not know that the light from 
Jupiter is less intense than the light from our moon, quantity for 
quantity. But I do not want to take this subject away from the im- 
mediate beariugs it may have on the former temperature of our 
planet. 
If the light and heat of sunshine be due to the frictional resistance 
of the earth's atmosphere to the waves of motion proceeding from the 
