COBEESPO> T L>E>-CE. 



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, which, 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, gloom} 7 , 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, which, together with the moon's heat, might 

 act as sufficient 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 Eendus,' 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,' 1863), 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 approaches 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 3600 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 affect (to such an 



