118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. DISCUSSION I 1 DISCUSSION. Professor Alfred W. Porter said that not having had the opportunity to see the paper before the meeting, what Principal Laurie had said came to him as rather a novel series of suggestions. With the need for re- cognising magnetic forces in the atom he fully agreed. The great weakness of the Bohr theory was the neglect of the magnetic side of the atom, although there was strong evidedce that it existed. A second weakness of the Bohr theory was that it is exceedingly difficult to conceive of the atom being an equilibrium system (or at least of a group of atoms forming an equilibrium system) when the electrons which play such an important part change in position from moment to moment.We could understand the theory better if the orbits were supposed to be stationary orbits, but that was not the supposition that Bohr had made. Therefore, it was exceedingly difficult to understand, on any principle of mechanics, how a system like that of Bohr could possibly be one which would remain in stable equilibrium. There was also evidence that the magnetic elements are small, and that had also been one of the fundamental assumptions made by Principal Laurie. The work that Oxley had done sufficiently showed the importance of these small stationary elements.On the other hand, if it is wrong to neglect the magnetic side, as Bohr does, it should be equally wrong to neglect the electric side, as Principal Laurie has done. There were two systems of forces present in the molecule, and he defied anyone to work out, on mechanical lines, the stability of a proposed atom unless both were taken into account. He would like to point out that in the actual model shown, the equilibrium was in part maintained by the wovden framework and not wholly by magnetic forces. If these wooden supports were removed, what were the magnetic orbits going to do ? The rigid framework completely altered the conditions of equilibrium. With regard to the actual success of the suppositions made by Principal Laurie in co-ordinating the various facts of chemical combination, it was impossible to estimate without further consideration.Perhaps, when he had had a chance of reading the paper he would be able to form a more definite conclusion. At the present time he would assert only that in his opinion all suggestions ought to be welcomed in regard to this matter because he did not think we were yet anywhere near finality concerning it. Dr. B. Flurscheim said that in view of the remarkable success achieved by the Bohr theory Principal Laurie’s attempt to connect this theory with the chemical properties of the atom appeared to be very interesting. Electrostatic theories of chemical combination had hitherto failed to account satisfactorily for the alternation of forces in organic chains.The introduction of a substituent caused an alternating increase and decrease in the amount of chemical force used up in successive bonds in a chain. This was evidenced by thousands of facts, and was recognised more and more by organic chemists. If Principal Laurie’s magnetic theory of chemical combination could account for these facts, then it would constitute a distinct advance. The President said he thought Professor Porter was right when he said that all suggestions should be welcomed and he was sure all those present had listened with much interest to the fascinating account which Principal Laurie had given, although there had not been time to study it. I t should be appropriate for the Faraday Society, bearing the name of such a founder, to learn of further examples of the connection between Could it account for them?12 SUGGESTIONS FOR A MAGNETIC THEORY OF VALENCY magnetism and rotation.These magnetic phenomena are now being taken into account by those who are considering the structure of the atom. H e had noticed recently a reference to experiments by Stern and Gerlack 1 who projected atomic silver through a non-uniform magnetic field on to a glass plate, and found that there were two spots of silver on the plate instead of one. This deflection they found to be due to the atom of silver possessing a magnetic moment, which sets itself parallel to or anti- parallel to the magnetic field, i.e. the two moments are at right angles to one another.If this is the case with the silver atom, it is very probable that the same thing will be found to hold with the atoms of other elements. Principal Laurie, in replying to the comments that had been made, said that it must not be assumed that he was ignoring the presence of the electrostatic forces because he had emphasised the importance of the magnetic forces in explaining chemical combination. Professor Porter would realise that it would be necessary in considering both these forces to give the right values to each of them, and he had felt that any attempt to do that at our present stage of knowledge would lead one into serious difficulties. H e had, therefore, preferred to treat the matter qualitatively and avoid all attempt at quantitative calculations which would involve the consideration of the electrostatic as well as the electro-magnetic forces.Professor Porter : Are they not equally in balance with one another? Principal Laurie continuing said that probably the electrostatic forces were varying as the inverse square of the distance and the magnetic forces as the inverse of the fourth power of the distance, consequently, their relative importance would change rapidly according to the distance between the atoms. What Professor Porter had said was probably true if it were assumed that the electrons were moving in circles between the nuclei of the atoms in combination as he had shown from his diagrams and models. If the electrons are moving in circles between the nuclei the result must be to produce a varying magnetic field which would mean that at one instant the atoms were held together much more strongly than at another instant. Such a view of the varying force of attraction would do much to explain the interchanges taking place when salts were present together in solution and to give the final explanation of this equilibrium of interchange which was known as the law of mass action. There was another possibility introduced by this view of a varying magnetic field and that was that in order for two atoms to combine the two vibrating magnetic fields must be in tune one with the other. This might explain one of the most curious facts which was constantly present to the chemist and that was the selective character of chemical combination. Zeit. Physik, 7, 85 (1921) ; 9, 345, 353 (1922) ; Physicu, 2, 122 (1922).