THE CONSTITUTION OF MATTER 127 



motion of the swift alpha and beta particles into heat, and is thus in a 

 sense a secondary effect of the radiations. The enormous emission of 

 energy is most simply illustrated by considering the case of the radium 

 emanation together with its swiftly changing products, radium A, 

 radium B and radium C. The heating effect of a given volume or 

 weight of this gas has been accurately determined. From the data, it 

 can be calculated that one pound weight of the emanation would emit 

 heat energy initially at the rate of 23,000 horse power. The rate of 

 emission decreases with the time, falling successively to half value after 

 intervals of 3.85 days. During the life of the emanation the total 

 energy emitted corresponds to an engine working at 128,000 horse 

 power for one day. Such a quantity of emanation would be an enorm- 

 ously concentrated source of power, for the total energy emitted is 

 many million times greater than for an equal weight of the most power- 

 ful known explosive. 



The emission of energy from radioactive substances does not con- 

 trovert the law of the conservation of energy ; for the energy is derived 

 from the atom itself where it exists in kinetic or potential form. We 

 shall see later that the atom is believed to consist of a large number of 

 positively and negatively charged particles which are collected in a very 

 small volume and held together by intense electrical forces. Such an 

 idea of atomic structure involves the necessity of a large store of energy 

 resident in the individual atom. The great emission of energy from a 

 radioactive substance like the emanation illustrates in a striking way 

 the enormous reservoir of energy that must exist in the atoms them- 

 selves ; for there is every reason to believe that an equivalent amount of 

 energy is present in the atoms of the common heavy elements. This 

 store of energy ordinarily does not manifest itself and is not available 

 for use. It is only when there is a drastic rearrangement of the atom 

 resulting from an atomic explosion that part of this store of energy is 

 liberated. 



It must be borne in mind that the processes occurring in radio- 

 active matter are spontaneous and uncontrollable. There is at present 

 no evidence to indicate that we shall be able in any way to influence 

 radioactive changes. We are at present only able to watch and in- 

 vestigate this remarkable phenomenon of nature without any power of 

 controlling it. In a recent book, H. G. Wells has discussed in an 

 interesting way some of the future possibilities if this great reservoir 

 of energy resident in the atoms were made available for the use of 

 man. This will only be possible on a large scale if we are able in some 

 way to alter the rate of radioactive change and to cause a substance like 

 uranium, or thorium, to give out its energy in the course of a few hours 

 or days instead of over a period of many thousands or millions of years. 

 The possibility, however, of altering the rate of transformation of 



