COBEESPOKDENCE. 
173 
hypothesis, and assume the existence of a sustained or continually acting 
motive power ? 
Then, recalling to mind the correlation of the physical forces, and view- 
ing heat and the other forces as directly or indirectly convertible into their 
equivalents of motion, we are induced to ask, may not force emanating 
from the sun be the sustaining cause of planetary centrifugal motion ? 
Here we should have a continuous supply of force, \a hich, by counteract- 
ing the centripetal force and the resistance of ether, would prevent any 
contraction of the orbits. Moreover, by such means, we could understand 
how it is that planets nearer the sun have a greater velocity than those 
more distant, for the increase of heat and consequently of velocity they 
received would be equal to the increase of attraction, and heat, velocity, 
and attraction would all be inversely as the square of the distance of the 
body from the sun. This we find to be the case. 
According to such a view, our journey around the sun would only cease 
when that luminary failed to supply the necessary amount of force. But, 
were the sun to become dark and cold, no life could exist on our globe, no 
changes could take place in the conditions of matter, there could be no 
liquids, no gases, so that the contact of earth and sun at such a time would 
be the collision of two dark, gloomy, silent, lifeless masses of inert 
matter. 
The revolution of satellites around planets, as for example that of the 
moon around the earth, might perhaps be accounted for by supposing the 
earth's motion (which we cannot believe to be wasted), converted into 
frictional heat at the surface, ^^hich, together with the moon's heat, might 
act as sullicieut centrifugal force to counteract their mutual attraction. 
The moon's revolution, in conjunction with the earth, around the sun 
would be perhaps the result of that luminary's heat or force acting on 
planet and satellite as a connected system. 
The greatest difficulty which presents itself to the view of solar force 
producing motion is the fact that we only know heat as a molecular force. 
But M. Faye, in the ' Comptes liendus,' supposes the existence of a repul- 
sive force exerted by the sun, not to be expressed by attraction with a 
negative sign prefixed, but bearing the same relation to molecular repul- 
sion as celestial attraction does to terrestrial attraction. 
Lastly, let us call the comets into the witness-box, and see what those 
eccentric individuals have to say on this subject. In an article entitled 
'* Cometary Phenomena" ('Intellectual Observer,' 18G3), we find the 
following : — " It is evident that the whole of the mass is vehemently 
acted upon by some influence emanating from the sun, the continuation 
and accumulation of which, after the perihelion passage, seem to point 
to a calorific rather than a more instantaneous electric or magnetic action." 
Again, Mr. Marsh, in writing of comets in the 'American Journal of 
Science and Arts,' attributes the peculiar character of cometary matter to 
the extreme and violent changes which it undergoes in its rotation around 
the sun. Halley's comet, for example, at one time ap])roaches the sun to 
within 56 millions of miles, and then recedes to the enormous distance of 
3370 millions of miles. At the time of its perihelion, or least distance, it 
passes through one heliocentric degree of its orbit in 15'7 hours, and receives 
in a given time 3G00 times as much heat as when it reaches its aphelion or 
greatest distance, in which position its motion is so slow, that six years 
and a half are required for its passage through one heliocentric degree. 
Thus, it will be seen, that comets with eccentric orbits are subject to vio- 
lent changes of temperature and velocity which do not afiect (to such an 
