LONDON. Royal Society, December 4.—Sir J. J. Thomson, president, in the chair.—A. M. Williams: The adsorption 'of gases at low and moderate concentrations. Part i.: Deduction of the theoretical adsorption iso-stere and isotherm. Part ii.: Experimental verification of the form of the theoretical isosteres and isotherms.—A. M. Williams: The adsorption of gases at low and moderate concentrations. Part iii.: Experimental verification of the constant in the theoretical adsorption isostere.—T. R. Merton: The secondary spectrum of hydrogen. It has been found that the presence of a large quantity of helium in vacuum tubes containing hydrogen modifies the secondary hydrogen spectrum in the sense that the relative intensities of the lines are completely altered, some lines being extremely weak in the spectrum of the mixture, whilst others are greatly enhanced and a number of new lines appear. Measurements have been made of the lines which are enhanced or unaffected by the admixture of helium; the changes are shown in a reproduction of a photograph of the two spectra in juxtaposition with a wave-length scale, by means of which the lines which are weaker in the spectrum of the mixture can be identified by reference to Watson's measurements of the spectrum. The secondary hydrogen spectrum is of such complexity that the segregation of its lines into series of mathematically related lines is a task which offers great difficulties. These difficulties can doubtless be lessened by the aid of physical methods of separating the lines into different classes.—T. R. Merton: The spectra of isotopes, (1) Interferometer measurements of the principal line in the spectrum of ordinary lead and lead from pitchblende show that in the latter case the line is less refrangible by 0.0050 A. ±0.0007 A., in close agreement with the results of Aronberg. (2) In the case of lead from Ceylon thorite it has been found that the line is more refrangible than in ordinary lead by 0.0022 A. ± 0.0008 A. (3) The positions of the lines are arranged in the order of their atomic weights. (4) Spectro-scopic measurements seem to provide a favourable method of distinguishing isotopic elements. (5) A comparison has been made of the wave-lengths of the principal line in ordinary thallium1 and thallium from pitchblende residues. The wave-length of the line in the spectrum of thallium from pitchblende has been found to be more refrangible than the line in ordinary thallium by 0.0055 A. ±0.0010 A. In the case of thallium the measurements may possibly be affected by certain disturbing factors which do not apply to the measurements of the lines of lead. Unless the results are affected by these disturbing factors, it would seem likely that the thallium in pitchblende is an isotope of ordinary thallium.—E. F. Armstrong and T. P. Hilditch: A study of catalytic actions at solid surfaces. Part ii. It is shown that the catalytic action of metals, like that of certain enzymes, is reversible; in other words, compounds which are saturated in the ordinary sense are capable of interacting with the metal to form a system which breaks down into a more stable equilibrium consisting of hydrogen and a less saturated compound. This is readily demonstrated in the case of cyclohexanol; when a mixture of cyclohexanol and methyl cinnamate' is heated at 180° in presence of nickel, a considerable transference into cyclohexanone and methyl β-phenyl propionate is effected. It is necessary that both components of the system should be present in the liquid state. Dehydrogenation has also been effected in the case of hexahydroxylene and dihydropinene mixed with methyl cinnamate in presence of nickel; in these cases a temperature of 230° is required. At this tempera'ture' small quantities of an ethyl oleate of unknown structure are obtained from ethyl stearate.—F. Horton and Ann C. Davies: An experimental determination of the critical electron velocities for the production of radiation and ionisation on collision with argon atoms. The critical velocities for electrons in argon were investigated by methods similar to those employed in a; previous research for the determination of trie corresponding values in helium, the earlier form of apparatus being modified somewhat to facilitate the detection of the beginnings of radiation and ionisation. As the result of many experiments under different conditions, the values 11.5 volts and 15.1 volts were obtained for minimum radiation velocity and minimum ionisation velocity respectively. No sudden increase of radiation at the second critical velocity was detected, and it was shown that no detectable amount of ionisation was produced at 11.5 volts, fhe limiting wavelength of the argon spectrum, calculated from the value, 15.1 volts, found for the minimum ionisation velocity, is in agreement with the limit observed spectroscopically in the recent experiments of Lyman.