656 



SCIENCE 



[N. S. Vol. XLIV. No. 1141 



rays, canal rays, the Zeeman effect in the 

 spectrum, X-rays and radioactivity have 

 thrown a flood of light on the constitution 

 of matter, and we now know that the 

 atom is very complex in its structure. We 

 know that certain chemical elements are 

 undergoing changes which involve the ac- 

 tual disintegration of the atoms, a phenom- 

 enon accompanied by an evolution of 

 energy far greater than that of any other 

 known phenomenon. It has been definitely 

 determined that in the partial disintegra- 

 tion of the atoms, where the atomic mass is 

 reduced only a few per cent., there is set 

 free, in some cases, more energy in the 

 transformation of one pound of an element 

 than is set free in the combustion of 100 

 tons of coal. Notwithstanding this enor- 

 mous evolution of energy, these spontane- 

 ous, atomic disintegrations are apparently 

 uninfluenced by external conditions, and 

 move along with as much precision and law 

 as the movement of the stars in their orbits. 

 These remarkable phenomena and the inti- 

 mate relation of electricity, radiant energy 

 and chemical phenomena to atomic struc- 

 ture have brought the problem of the na- 

 ture of the atom into great prominence in 

 scientific literature. 



The experiments of Crookes on the elec- 

 tric discharge in high vacua may be said to 

 have opened the way for the experimental 

 evidence of the complex nature of the atom. 

 Pliicker, Hittorf, Goldstein and others had 

 previously investigated this subject, but the 

 results did not become far reaching in 

 their influence on scientific theories until 

 Crookes published the results of his earlier 

 observations in 1879. He found that, re- 

 gardless of the nature of the residual gas 

 in the exhausted tube or the nature of the 

 cathode, the rays which are given off at the 

 cathode consist of particles moving in 

 straight lines, that they produce a brilliant 

 glow on phosphorescent substances, that 

 they exert a mechanical force and generate 



heat rapidly when intercepted, and that 

 their trajectory is altered by the influence 

 of a magnet. 



Crookes did not carry these experiments 

 to a successful conclusion, but so remark- 

 able were the results that he concluded that 

 the particles of the cathode rays represent 

 a fourth state of matter which he called 

 radiant matter. He said: 



We have actually touched the borderland where 

 matter and force seem to merge into one another. 

 I venture to think that the greatest scientific prob- 

 lems of the future -will find their solution in this 

 borderland and even beyond. 



In a later communication he spoke of the 

 "ultimate or rather ultimatissimate par- 

 ticles moving with incredible velocity," 

 and of the possibility that elements with 

 atomic weights higher than that of ura- 

 nium might dissociate into simpler atoms. 

 These statements were certainly prophetic 

 of the important discoveries which were to 

 follow. 



Hertz and Lenard showed that the cath- 

 ode rays would pass through thin plates 

 of metal. They concluded that these rays, 

 owing to their penetrating power, were a 

 form of radiant energy. Later investiga- 

 tion, however, showed the Lenard rays to 

 be identical with the cathode rays, and that 

 both are due to moving particles. 



The discovery of X-rays by Eontgen in 

 1895 gave a great impetus to the investiga- 

 tions on the electric discharge in high 

 vacua. "When the cathode rays are sud- 

 denly stopped by matter of any kind X- 

 rays are produced. These rays are a form 

 of radiant energy. The X-rays apparently 

 originate in the interior of the atom, and 

 each atom emits X-rays which are charac- 

 teristic of its own structure. This subject 

 will be referred to again. 



Omitting some less important observa- 

 tions, we now come to the work of J. J. 

 Thomson, 1897. He determined experi- 

 mentally that the particles of the cathode 



