m REFORMED CONCEPT OF MATTER 39 



atomic weights and the properties of atoms. These triumphs 

 were reserved for the New Physics, and they have traced 

 structure back into the innermost recesses of the atom. The 

 discovery of Radioactivity by Becquerel in 1896 at Paris 

 was the first indication that the atom was not indivisible and 

 could break up spontaneously in nature. The discovery in 

 the previous year of the X-rays by Rontgen for the first time 

 revealed the existence of invisible rays whose wave-length 

 was as small as atoms, and the elaboration of the spectrum 

 of these rays has provided an instrument of incredible power 

 and accuracy in the investigation of the almost infinitesi- 

 mally small phenomena of atomic structure. Then followed 

 in 1899 the isolation by Sir J. J. Thomson of the ultimate ' 

 unit of negative electricity in the electron; and in the fol- 

 lowing year Max Planck of Berlin University discovered 

 what came to be known as the quantum, the unit of radiant 

 action emitted by all radiant bodies or even dark bodies. The . 

 application of these new ideas and means of investigation by 

 a number of brilliant researchers has led to the elucidation 

 of the nature and constitution of the atom of matter in the 

 theory which is specially associated with the names of Sir 

 Ernest Rutherford and Professor Niels Bohr. Without en- 

 tering into details which do not concern us, and simply to 

 illustrate the element of " structure " in the atom with which 

 we are dealing, I shall summarise the salient points in this 

 theory. According to it, an atom is an electrical constella- 

 tion somewhat like our gravitational solar system; the centre 

 of the system being a minute very massive nucleus positively 

 electrified, round which revolve equally minute electrons or 

 negative particles of very small mass — so small that in the 

 Hydrogen atom, for instance, the nucleus has 1835 times the 

 mass of the electron. The electrons revolve at various rates 

 in their different orbits, all of which can be measured 

 through their X-ray spectrum; and an electron can suddenly 

 and all at once jump from one orbit to another, increasing its 

 orbit when it receives one or more quanta of radiation from 

 some outside body, or decreasing its orbit and taking one 

 nearer the central nucleus, and in the act of doing so releas- 



