4 



THE GEOLOGIST. 



alteration from remarkable former conditions of our planet. Let ns 

 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 

 checked. 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 ? 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 bearings 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 



