NEW CONCEPTIONS IN SCIENCE 



cold. That is highly probable. Men's minds 

 have varied in their notions as to what heat 

 is. It used to be thought a substance. But 

 briskly rubbing together two pieces of ice produces 

 heat enough to melt both. If mere friction can 

 produce heat, it is evidently a form of motion and 

 not a material thing. That is the way it is now 

 regarded. If space is not warmed by the heat of 

 the sun and the stars, then heat is the motion of 

 something else than the material of space, if there 

 be such. 



We know of heat only as it is associated with 

 what we call matter, and since all bodies, when 

 made hot enough, turn to vapor and fly away in the 

 air, heat is thought to be the motion of these very 

 small particles. To send out the measured waves 

 of heat and light, these particles would have to vi- 

 brate at a rapidity beyond anything we can con- 

 ceive. 



Waves of light reach the eye at the rate of 450 

 to 750 million millions per second. The particles 

 of matter would have to vibrate the same number 

 of times to send these waves out. The number is 

 so unthinkable that one might get the notion that 

 there is no limit. That may be, but, in view of the 

 finite nature of observed phenomena, it is quite pos- 

 sible there is a limit. There is reason for believing 

 that heat is the motion of the individual atoms, 



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