MASS SPECTRA OF THE ELEMENTS ASTON. 225 



values. Since both the cathode rays and the positive rays are 

 streams of separated electric charges, they may be deflected by sub- 

 jecting them to the influence either of an electric field or a magnetic 

 field. In an uniform magnetic field, at right angles to their path, 

 the cathode rays move on the arc of a circle so that the plane defined 

 by the original ray and the magnetically deviated one is at right 

 angles to the lines of magnetic force. A somewhat similar devia- 

 tion may be brought about by an electrostatic field produced by 

 two metal plates parallel to the magnetic field and to the original 

 cathode ray, one plate above the other beneath the beam, and main- 

 tained at a suitable difference of electrical potential. 



To deflect equally the positive raj's requires very much stronger 

 magnetic or electric fields than suffice for cathode rays. For the 

 masses of the electrified particles in the positive rays are thousands 

 of times greater than the masses of the negative ions which compose 

 the cathode rays. 



As the result of investigations of the last 25 years of vacuum- 

 tube phenomena, radioactive substances, and in other related 

 branches of inquiry (see the papers of Millikan, Rutherford, and 

 Eve above cited), a rapidly penetrating and clarifying view of 

 the structure of the atom and its relations to electrical and chemi- 

 cal phenomena has come about. Progress is so rapid that what was 

 written 10 or even 5 years ago no longer quite fits all of the obser- 

 vations, and what I am about to write will doubtless not long be a 

 fully representative statement. Even now Doctor Langmuir's views 

 are not harmonized to it. At the present, however, to meet the re- 

 quirements of the physicists' observations one may view an atom as 

 having a central nucleus whose mass comprises almost the whole 

 mass of the atom, but whose volume is perhaps as small, compared 

 to the whole volume of the atom, as that of the sun is to the solar 

 system. Outside the nucleus, in one or several orbits comparable 

 to the orbits of the planets, revolve the negative electrons or ions. 

 The number of outside ions which an atom holds is equal to the 

 Moseley atomic number. Some negative ions may also be agglomer- 

 ated in the nucleus. But the main mass of the nucleus is composed 

 of the so-called positive particles. Of these the hydrogen atom has 

 one, and heavier atoms a plurality. This agglomeration which we 

 call the nucleus has a positive charge equal to the sum of the nega- 

 tive charges of the outlying ions. When under the influence of an 

 electric field one of the outlying ions may be knocked off and pro- 

 ceeds toward the anode, while the remainder of the atom proceeds 

 toward the cathode. A molecule comprising two or more atoms, 

 such as hydrochloric acid (HC1) or carbonic acid (C0 2 ), is a still 



42803°— 22 15 



