160 Mr. S. T. Preston on the Continuance of 



be far greater than 20 or 30 million years, we prove that 

 there must have been some other source in addition to gravity 

 from which the sun derived his store of energy." The colli- 

 sion of matter in translator^ motion is then suggested as the 

 only conceivable other source of the store of heat-energy in 

 the sun — this suggestion having already been made by the 

 same author in a previous paper published in the Philosophi- 

 cal Magazine for May 1868, where it is remarked (p. 373): — 

 " The Dynamical Theory of Heat affords an easy explanation 

 of at least how such an amount of energy may have been com- 

 municated. Two bodies, each one half the mass of the sun, 

 moving directly towards each other with a velocity of 476 

 miles per second, would by their concussion generate in a 

 single moment 50,000,000 years' heat - " [i e. an amount of 

 heat which would cover the present rate of the sun's radiation 

 for a period of 50,000,000 years]. 



It would seem to be scarcely realized what a field for rapi- 

 dity of motion combined with all the stability or permanence 

 of apparent rest the universe presents. It is a mere question 

 of scale for bodies to possess any velocities (no consequence 

 how great), and yet not alter their relative positions appreci- 

 ably in a given epoch of time. Thus a stellar mass, for ex- 

 ample, that moved transversely to the observer a distance 

 equal to its own diameter [say a million miles, which is roughly 

 the sun's diameter] in a second, would appear to the eye to be 

 at rest; for the disk of the stellar mass has no apparent dia- 

 meter even in the best telescope, and therefore the distance 

 moved in a second would be invisible. Yet the velocity of 

 the stellar mass in that case would be about five times that of 

 light*. Dr. Croll has pointed out (Phil. Mag. July 1878) that 



* Since light requires a quarter of an hour to traverse the diameter of 

 the earth's orbit, and since that diameter (182,000,000 miles) would be a 

 point when viewed at the distance of the nearest star, it follows that, if 

 the nearest star were moving transversely to the observer with the velo- 

 city of light, the star might be watched for a quarter of an hour without 

 appearing to deviate from its position. The actual angular distance tra- 

 versed by the star, after the motion equal to that of light had been going 

 on for a quarter of an hour, would be the thickness of a human hair held 

 at 25 feet from the eye [this being the known representation of an angle 

 of 2 seconds, which is that subtended by the earth's orbit at the distance 

 of the nearest star]. This star might move with the velocity of light for 

 1\ hours without traversing a greater angular distance than the thick- 

 ness of a hair held 10 inches from the eye. 



The tendency of modern science is unquestionably to look to a dyna- 

 mical interpretation of phenomena in place of the old vaguely conceived 

 statical ideas. The old tendency has been rather in the direction of igno- 

 ring the motions of the stellar masses, and of banishing from the concep- 

 tions (in the attempt to arrive at some notion of stability in the universe) 

 all idea of a direct interference or mutual action of the moving parts of the 



