236 REPORTS ON THE STATE OF SCIENCE. — 1920. 



With still more complex molecules it becomes necessary to accept the exist- 

 ence of small atomic groupings within the principal groupings. Without going 

 into the resulting system in detail it may be stated that this will result in 

 the sub-division of the sub-groups into ismaJler sub-groups. It is of considerable 

 interest to note that the phosphorescence and absorption bands shown by certain 

 uxanyl compounds exhibit this type of structure. ^^ 



Before entering further into the quantitative relationships one point arising 

 from the foregoing discussion of energy quanta may be mentioned. It has been 

 .shown that in the water molecule the oxygen atom exhibits two characteristic 

 frequencies and the hydrogen atom one, whilst in sulphur dioxide the oxygen 

 atoms exhibit one and the sulphur atom two characteristic frequencies. It is 

 difficult to avoid the conclusion that the characteristic atomic frequency is the 

 basis of the valency of that atom. Thus a univalent atom may be one for 

 which there is only one possible shift of its electrons, "with a bivalent atom 

 there may be two possible shifts, and so on. From this it would also follow 

 that the numerical size of the elementary quantum associated with the atoms 

 of an element determinee the position of that element in the series of electro- 

 positivity. Obviously the larger the elementary quantum associated with an 

 atom the greater will be the energy given out when that atom enters into 

 combination. Further, when a multivalent atom enters into successive com- 

 bination with atoms of a given univalent element, its largest elementary quantum 

 will be concerned when it combines with the iirst atom. This will be followed 

 by the next largest, and so on. This will mean that the ' strength ' of its 

 different valencies will be different, and the individual bonds with the various 

 atoms of the univalent element will require different amounts of energy to 

 resolve them. 



There now remains to be considered the origin of chemical reaction. The 

 relationships between the frequencies shown by a molecule and its component 

 atoms have been discussed, but nothing has been said as to why atoms combine 

 together and why certain specific propei'ties are associated with the molecules 

 produced. It would seem that the key to this problem is to be found in the 

 electromagnetic force fields of the atoms. It is evident that, according to 

 the modern view of atomic structure, a central positive nucleus with negative 

 electrons in rotation round it, each atom must form the centre of an electro- 

 magnetic field of force. These force fields were first dealt with by Humphreys, 23 

 who showed that they are capable of giving a quantitative explanation of the 

 Zeeman effect and also of the pressure-shift of spectrum lines. He deduced 

 the fact that two atoms wiU attract one another when they approach in such 

 a way that the direction of their electronic motions is tlie same, and will repel 

 one another when their electronic motions are in opposite directions. Each 

 atom therefore possesses two faces, and when one pair of faces comes together 

 they repel one another, and when the other pair comes together they attract 

 one another. In other words, an atom forms the centre of an electromagnetic 

 field of force, the opiJosite poles of which, are localised in two opposite faces 

 of the atom. 



Let it be supposed that two atoms of different elements are brought together 

 in such a way that their mutually attracting faceis come together. They will 

 at once tend to form an addition complex which can lose energy in the 

 maimer already described. The two atoms radiate equal amounts of energy 

 as a whole number of elementary quanta whereby the resulting molecule becomes 

 endowed with the frequency based on the least common multiple of the atomic 

 frequencies. This molecule is now rendered a stable entity, and can only be 

 Tesolved iiito its atoms by absorbing an am.ount of energy equal to that lost 

 in its formation. This quantity of energy consists of a definite number of true 

 molecular quanta. 



As will be noticed, however, in this suggestion, that the reactivity of atoms 

 for one another is due to the attraction of their respective force fields, and 

 that their combination consists in their joint loss of equal amounts of energy, 

 no account has been taken of the other faces of these combining atoms. Whereas 

 the combination of the atoms produces a molecule characterised by a specific 

 energy quantum, it is not possible to consider that the force fields due to the 

 external atomic faces can exist without influence on one another. These 

 external force lines must condense to form an external molecular force field, and 



