Septembeb 3, 1909] 



SCIENCE 



299 



tance as a subdivision of matter whose 

 properties should be exhaustively studied. 



The proof of the existence of corpuscles 

 or electrons with an apparent mass very 

 small compared with that of the hydrogen 

 atom, marks an important stage in the ex- 

 tension of our ideas of atomic constitution. 

 This discovery, which has exercised a pro- 

 found influence on the development of 

 modern physics, we owe mainly to the 

 genius of the president of this association. 

 The existence of the electron as a distinct 

 entity is established by similar methods 

 and with almost the same certainty as the 

 existence of individual a particles. While 

 it has not yet been found possible to detect 

 a single electron by its electrical or optical 

 effect, and thus to count the number 

 directly as in the case of the a particles, 

 there seems to be no reason why this should 

 not be accomplished by the electric method. 

 The effect to be anticipated for a single )3 

 particle is much smaller than that due to 

 an a particle, but not too small for meas- 

 urement. In this connection it is of inter- 

 est to note that Regener has observed 

 evidence of scintillations produced by the 

 yS particles of radium falling on a screen of 

 platinocyanide of barium, but the scintil- 

 lations are too feeble to count with cer- 

 tainty. 



Experiment has shown that the apparent 

 mass of the electron varies with its speed, 

 and, by comparison of theory with experi- 

 ment, it has been concluded that the mass 

 of the electron is entirely electrical in ori- 

 gin and that there is no necessity to as- 

 sume a material nucleus on which the 

 electrical charge is distributed. While 

 there can be no doubt that electrons can be 

 released from the atom or molecule by a 

 variety of agencies and, when in raipd mo- 

 tion, can retain an independent existence, 

 there is still much room for discussion as 

 to the actual constitution of electrons, if 

 such a term may be employed, and of the 



part they play in atomic structure. There 

 can be little doubt that the atom is a com- 

 plex system, consisting of a number of 

 positively and negatively charged masses 

 which are held in equilibrium mainly by 

 electrical forces ; but it is difficult to assign 

 the relative importance of the role played 

 by the carriers of positive and negative 

 electricity. While negative electricity can 

 exist as a separate entity in the electron, 

 there is yet no decisive proof of the exist- 

 ence of a corresponding positive electron. 

 It is not known how much of the mass of 

 an atom is due to electrons or other moving 

 charges, or whether a type of mass quite 

 distinct from electrical mass exists. Ad- 

 vance in this direction must be delayed 

 until a clearer knowledge is gained of the 

 character and structure of positive elec- 

 tricity and of its relation to the negative 

 electron. 



The general experimental evidence indi- 

 cates that electrons play two distinct roles 

 in the structure of the atom, one as lightly 

 attached and easily removable satellites or 

 outliers of the atomic system, and the 

 other as integral constituents of the inter- 

 ior structure of the atom. The former, 

 which can be easily detached or set in vi- 

 bration, probably play an important part 

 in the combination of atoms to form mole- 

 cules, and in the spectra of the elements; 

 the latter, which are held in place by much 

 stronger forces, can only be released as a 

 result of an atomic explosion involving the 

 disintegration of the atom. For example, 

 the release of an electron with slow veloc- 

 ity by ordinary laboratory agencies does 

 not appear to endanger the stability of the 

 atom, but the expulsion of a high speed 

 electron from a radioactive substance ac- 

 companies the transformation of the atom. 



The idea that the atoms of the elements 

 may be complex structures, made up either 

 of lighter atoms or of the atoms of some 

 fundamental substance, has long been fa- 



