40 HOLISM AND EVOLUTION chap. 



ing one or more quanta of radiation. It is these quanta of 

 radiation, released when the electron jumps to a narrower 

 orbit in the atom, that account for the light which comes 

 from the sun and the stars, and in fact all radiant bodies; 

 and it is the definite quanta of radiation so emitted which 

 account for the peculiar spectrum of the elements in the 

 spectroscope. Why atomic light should be emitted in these 

 definite amounts or quanta is not yet known, but it is known 

 that the quanta follow a scale somewhat similar to the notes 

 in music, and we may therefore think of light as the music of 

 the spheres, in which the total harmony or light effect is 

 made up of definite discontinuous notes instead of continu- 

 ous variations of light. The wonderful thing is that in 

 regard to all these matters we have the most minute and 

 accurate knowledge: the amount of a quantum; the mass, 

 velocity and orbits of an electron; the mass and velocity of 

 rotation of a nucleus, and the total sphere of an atom, with 

 its small nucleus and electrons and vast empty spaces, com- 

 parable to the empty spaces in our solar system. The elec- 

 tron is by now very well known, and indeed all electric cur- 

 rents are nothing but streams of free electrons. But of the 

 corresponding positive unit which is called a proton next to 

 nothing is known, as the proton has never yet been isolated. 

 Now the nucleus of an atom may be simple or complex; it 

 may be a proton, as in the case of the Hydrogen atom, or it 

 may consist of several protons, some of which, again, may be 

 neutralised by closely associated electrons, and some remain 

 unneutralised, so that the nucleus as a whole always remains 

 positively electrified. In the Hydrogen atom there is one 

 proton in the nucleus, and hence there is one electron revolv- 

 ing round it. In the Helium atom, again, there is a 

 nucleus of four protons, two of which have electrons in as- 

 sociation with them, and two not; the nucleus, therefore, 

 has two positive units, to which correspond two electrons 

 which revolve round the nucleus in the atom. The com- 

 bination of four protons and two electrons in the Helium 

 nucleus appears to persist in other nuclei, so that the nuclei 

 of the other elements appear to be a combination of simple 



