A PREAMBLE ON ENERGY 57 



{ii) In the outer universe. In the radiant energy of the stars, 

 appearing to us as Hght and heat ; 



In cosmic radiations traversing space in all directions ; 

 In universal gravitation. 



17. ON MATERIAL THINGS AND ENERGIES 



The universe is constituted by material things and energies 

 (this statement is of the nature of a first approximation). What- 

 ever they may be, material things are constituted by about ninety- 

 five different kinds of chemical atoms. 



Whatever kinds they may be, the chemical atoms are constituted 

 by protons and electrons. 



Electrons are indivisible, excessively minute charges of electri- 

 city, negative in their sign. Protons are corpuscles constituted 

 in some unknown way and exhibiting a positive sign. In some 

 way protons become aggregated to form the nuclei of atoms 

 and round the atomic nucleus there is an " atmosphere " of 

 " satellite " electrons. The latter are distributed in *' orbits," 

 but close to the nucleus an electron fills the whole orbit. At a 

 great distance from the nucleus the satellite electrons behave 

 as particles which are regarded as revolving round the nucleus 

 in orbits. They may also behave as waves. There can only be 

 a limited number of such orbits and an electron can change 

 its orbit. But it disappears from one orbit and simultaneously 

 appears in another rather than " jumps " from one orbit to 

 another. 



Different kinds of atoms are characterized by having different 

 numbers of protons in their nuclei and different numbers of 

 satellite electrons. 



Protons and electrons are electricity and electricity implies 

 energy. Therefore the physical substance of the universe is 

 energy. 



18. ON RADIATION 

 Radiation is energy that is not inherent in, or immediately 

 associated with material bodies. Familiar examples are : 

 The heat felt when one stands near a fire ; 

 The light coming from the sun ; 

 Wireless signals. 



i8«. Fields of Force. There is said to be magnetism in 



