150 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1925 



One suggestion is that by collision of a very infrequent type be- 

 tween an electron and a proton (the ultimate particles of matter 

 known to the physicist, carrying the unit electrical charges, negative 

 and positive) their impact results in complete annihilation of their 

 mass — that is, of tlie matter which they form — a definite amount of 

 radiant energy being the equivalent result. This is highly specula- 

 tive, there being no observed phenomenon in nature to prove 

 definitely that such a transformation can take place; but it is 

 theoretically possible, for matter and energy are essentially the same 

 thing. Matter is one of manj'^ forms of energy and in the usual 

 units of measurement of energy, the energy equivalent of a mass m 

 grams of matter is in c'- ergs where c is the velocity of light, 3X10^° 

 cm. per second. In other words, one gram of matter represents a 

 potential concentration of energy equivalent to nine hundred million 

 million million ergs, or as more conveniently expressed, 9X10"" 

 ergs; or one pound of matter embodies iX (186,000X5,280)- foot- 

 pounds of energy — that is, 10^^ foot-pounds. 



The theory of relativity has shown mathematically, and it has 

 been confirmed experimentally for fast moving alpha and beta 

 particles, that what we term mass is really a property of matter that 

 depends upon its velocity. Mass increases with increase of velocity, 

 but this increase only becomes apparent when the velocity is so great 

 that it becomes comparable to the velocity of light. The full expres- 

 sion for mass energy in the relativity theory is 



Here the first term is the whole intermolecular energy of the mass 

 at rest ; the second term is its kinetic energy, or the energ}^ possessed 

 by it in virtue of its motion; the third and subsequent terms will be 

 quite negligible for small values of the velocity v of the mass, but 

 become appreciable one by one as the velocity v approaches the 

 velocity of light. From this it follows that in order for the mass of 

 a star to diminish as a result (or perhaps we should say as the 

 cause) of its radiation, it is not necessary to postulate the annihila- 

 tion of matter, but simply the loss in mass resulting from loss in 

 velocity. From the above equation it can be seen that this might 

 well be a tremendous reservoir of available energy. 



The idea that continued stellar radiation might imply gradual loss 

 in stellar mass was not new. It had been suggested some years ago 

 by Dr. J. H. Jeans, but the facts above explained brought this idea 

 forward with a new significance. Doctor Jeans saw that if this idea 

 be really true, many astronomical problems are seen in a new light, 

 and many investigations require reconsideration. This he has done 

 and only recently has he published his results. 



