no Presidential Address 



of decadence when the sun and all bodies are at one and the 

 same temperature and when every activity has ceased. 

 (Cf. page 59.) The Universe is undoubtedly still a going 

 concern, and yet it has presumably already lasted an 

 infinite time for all we know to the contrary. 



As to the first law of Thermodynamics, that is merely 

 the conservation of energy applied to heat. It was the 

 experimental and quantitative inclusion of heat as a form 

 of energy which allowed the law of Conservation of Energy 

 to be definitely formulated by Joule. 



Page II 



The most important of Newton's Laws of Motion is 

 that the acceleration of a body is proportional to the 

 resultant force which acts upon it and is in the same di- 

 rection. The ratio of force to acceleration is called the 

 mass or inertia of the body, and in ordinary Newtonian 

 Mechanics it is treated as constant. There is a sense in 

 which the remarkable constancy of mass, no matter what 

 happens to it, in the way of boiling, freezing, decom- 

 position, burning, or solution, is synonymous with the 

 fundamental postulate of the conservation of matter. But 

 there are other senses in which it is not difficult to allow for 

 a possible variation of mass of a moving body, and hence to 

 get a variable ratio between the force applied to it and the 

 acceleration produced. 



Recently it has been found that electrons moving near 

 the speed of light have an increased mass. The result has 

 been arrived at both theoretically and experimentally. 

 It was in fact first predicted mathematically and after- 

 wards confirmed experimentally, and may be taken as 

 quite undoubted. 



Mass therefore becomes a function of speed. At all 

 ordinary speeds it is practically constant; but at excessive 

 speeds, far beyond that of a cannon ball, it begins very 



