NOTES 463 



ments of the masses of various atoms, illustrating his paper by excellent 

 slides. Many elements were shown to consist of two or more isotopes, 

 i.e. atoms having the same atomic number (or nuclear charge) but different 

 masses. Neon, for example, has at least two isotopes of masses 20 and 22 

 respectively ; krypton has six, and bromine, although its atomic weight as 

 determined chemically is almost exactly 80, is really a mixture in nearly 

 equal proportions of isotopes 79 and 81, thus containing none of mass 80. 

 Many new results may be anticipated in the near future. 



Sir E.Rutherford, in his paper on the Building up of A toms, recapitulated 

 his recent Bakerian lecture, showing how it was possible to eject hydrogen 

 atoms from nitrogen by a-ray bombardment, and to produce by similar 

 methods from nitrogen and oxygen a new atom of mass 3 and nuclear 

 charge 2 — an isotope of helium. He then proceeded to indicate how, 

 possibly, the central nuclei of various elements are built up of aggregations 

 of elementary positive charges and negative electrons. The fundamental 

 positive charge he regards as the nucleus of the hydrogen atom, i.e. a hydrogen 

 atom with the outer electron removed. [Sir O. Lodge subsequently suggested 

 that an entity of such importance should have a name and suggested " pro- 

 ton." This suggestion will be adopted in what follows.] A proton with an 

 electron closely attached to it would form an undiscovered element of mass 

 I and zero atomic number. Such an element would be likely to evade dis- 

 covery, since, having no attached electron at a comparatively great distance, 

 it would pass readily through all materials, and it would give no spectrum. 

 By suitable additions of protons and electrons to this nucleus, it is possible 

 to construct models having the correct masses and atomic numbers of the 

 elements. Thus four protons and two electrons would give the correct nucleus 

 for ordinary helium, whereas three protons and one electron would fulfil the 

 conditions necessary for the helium isotope already referred to. The latter, 

 according to Sir Ernest's model, is a very stable arrangement, and likely to 

 survive in the disintegration of nitrogen and oxygen nuclei by a-ray bombard- 

 ment. Sir Ernest insisted that speculation on this subject should not be 

 allowed too great freedom, but it appears likely that very important develop- 

 ments may be expected shortly. 



Prof. R. Whiddington read a paper on The Ultramicrometer. This con- 

 sists of a parallel plate condenser the variations of capacity of which are 

 observed by means of a heterodyne arrangement of oscillatory triode valves. 

 Variations of distance of only a two hundred millionth of an inch between 

 the plates are detectable by means of the change in the pitch of the " beat " 

 note. Sir O. Lodge and Mr. F. E. Smith criticised the results in relation to 

 their applicability to measuring actual distances, and the author replied, 

 indicating that great precautions were necessary in maintaining constancy of 

 temperature of the condenser, and of the frequencies of the oscillating circuits. 



Astronomical papers followed by Lt.-Col. F. J. M. Stratton on the 

 Spectra of Nova Aqulice III, and Father Cortie on Comparison of Drawings 

 of Solar FaculcB and Photographs of Calcium Flocculi. 



On August 26 the greater part of the session was occupied by a discussion 

 on the Origin of Spectra. This was opened by Prof. A. Fowler, who gave 

 a general outline of the various types of spectra obtained from the elements 

 and their representation by well-known formulae. The series into which the 

 lines fall were well illustrated by slides. Prof. J. W. Nicholson followed 

 with a description of Bohr's theory of atomic constitution and the production 

 of spectra. To this theory, with its subsequent modifications, particularly 

 by Sommerfeld, he has become converted, and he indicated the numerous 

 ways in which the theory has received support in observations. Prof. J. C. 

 McLennan added further evidence in favour of Bohr's theory by reference 

 to his own measurements of monochromatic spectra produced by electron 

 bombardment. The amounts of electron energy required for this purpose bear 



