SECTIONAL TRANSACTIONS.

SECTION A.-MATHEMATICAL AND PHYSICAL

SCIENCE.

(For references to the publication elsewhere of communications entered in the following list of transactions, see page 464.)

Thursday, August 7.

1. Prof. A. FOWLER, F.R.S.-The Spectra of Ionised Elements. The paper gives a summary of recent work on the spectra of ionised and multiple-ionised atoms. In the case of silicon, four successive spectra have been sufficiently observed to permit the complete or partial classification of the lines in series. In passing from Si IV to Si I, the effects of adding external electrons one by one are exhibited under somewhat simpler conditions than in the regular sequence of the neutral atoms of Na, Mg, Al, and Si, since the charge and the mass of the nucleus remain constant. Similar changes in the spectra of other elements have been observed, and series have been worked out for C II. The ionisation potentials deduced from the series of silicon and carbon have an important application in connection with the determination of the temperatures and densities of stellar atmospheres.

2. Dr. F. L. MOHLER and Dr. P. D. FOOTE.-Critical Potentials and their Interpretation.

Available data on the normal energy levels of atoms, particularly in the range inaccessible to spectroscopic methods, are summarised. Results obtained in this laboratory on radiation potentials of gases and stages in the excitation of spectra are compared with critical radiation potentials of solids and other data on soft X-ray limits. Moseley diagrams of these limits give curves of the type predicted by Bohr.

Some questions as to the interpretation of critical potentials can be settled on the basis of this correlation of results.

3. Prof. J. C. MCLENNAN, F.R.S.-Recent Studies in Band Spectra and their Bearing on the Structure of Molecules.

4. Mr. R. H. FOWLER.-Mechanisms of Excitation, Ionisation, and Dissociation in Statistical Theory.

This paper attempts a systematising survey of current theory and experimental evidence about the processes occurring, or mechanisms of exchange normally acting, in gaseous assemblies, particularly at high temperatures. Two different hypotheses form possible starting-points: (A) The hypothesis of preservation, that the actual distribution laws for the systems in any assembly in equilibrium must be the same whatever the mechanisms of exchange that are setting up this equilibrium; (B) The hypothesis of detailed balancing, that in equilibrium the effects of any specified process, or element of a process, must be balanced exactly by another which is the exact reverse of the one specified, differing, that is, only in a reversed time scale. These hypotheses are not equivalent, (B) being more restrictive than (A), and a number of mechanisms are re-examined explicitly in the light of these hypotheses, including the mechanism of excitation by collision (Klein and Rosseland), ionisation and dissociation by collision (Becker), excitation by radiation (Einstein), scattering by free electrons (Einstein and Ehrenfest), and the photo-electric effect (Kramers, Milne).

5. Dr. R. J. PIERSOL.-Pulling Electrons from Metals by Intense Electric Fields.

The tube contains electrodes made from molybdenum plates pressed into hemispherical shells, welded to tungsten rods which are sealed into a hard glass tube. The discharge gap is 0.023 cm. A charcoal bulb is attached which is kept at 386° C. The electrodes are heated to 1,400° C. by induction furnace, the tube is baked at 500° C., the vacuation covering forty-eight hours. The connected tube and bulb is sealed off. The bulb is placed in liquid air and the discharge tube is heated at 500° C. for two hours. Then the tube is slowly sealed off from the charcoal bulb. The critical gradient is 5,400 Kv/cm. This minimum potential is sharply defined, showing that proper outgassing completely eliminates field currents, thereby giving a definite gradient of cold electronic discharge.

6. Dr. ANN C. DAVIES.-The Metastability of the Fundamental Coplanar Condition of the Helium Atom.

Further experimental evidence bearing on the conclusions of Horton and Davies that an emission of radiation results from the displacement of an electron within a helium atom from the normal orbit (the fundamental orbit of the crossed system) to the first outer orbit (the fundamental orbit of the coplanar system), and that this radiation can be absorbed by normal helium atoms, these conclusions being at variance with the conception of the fundamental coplanar condition of the helium atom as a metastable state.

7. Prof. H. N. RUSSELL.-The Spectrum of Titanium.

8. Prof. FRANK ALLEN.-Visual Sensory Reflexes.

In endeavouring to discover the fundamental processes of colour vision, experiments were conducted by fatiguing the left eye with a series of monochromatic spectral colours and making measurements of the effects produced on the right eye. The method used was the measurement of the critical frequency of flicker. In these experiments the dark room was discarded and the eye was maintained in ordinary daylight adaptation. The results showed the existence of visual sensory reflexes, the chief effect of which is to enhance the sensitiveness of the receptors of all three fundamental colour sensations in the right eye.

In a similar manner the right eye was fatigued, and it was found that both direct and reflex effects were simultaneously produced. The simple colours-red, green and violet-affect one sensation directly and two reflexly. The compound colours-orange, yellow and blue-affect two sensations directly and one reflexly. No doubt all colours affect all three sensations both directly and reflexly, but the experiments give the net final results.

Similar experiments were tried by confining fatigue to one side of a retina and measuring the reflex effects produced on the other side. They were pre. cisely the same as in the binocular experiments.

The reflex principle seems to give an adequate explanation of a monocular and binocular contrast, positive and negative after-images, and the general phenomena of colour vision.

The results strongly confirm the three-components theory of Thomas Young.

9. Mr. F. J. W. WHIPPLE.-An Experiment Illustrating the Theory of the Green Flash.

When the sun sets under favourable conditions the last glimpse appears a brilliant green.

The theory that the phenomenon is due to the simultaneous action of dispersion and absorption is now generally accepted. The experiment is designed to illustrate this theory.

10. Sir RICHARD PAGET, Bart.-The Nature and Artificial Production of Speech Sounds.

The resonances heard in the lecturer's own whispered vowel sounds were compared with those obtained by instrumental methods by Dr. D. C. Miller ('Science of Musical Sounds,' 1916, Lecture VII, page 235 et seq.).

The double resonances obtained by Miller for the vowel sounds mat, met, mate, meet, were shown to be comparable with the lecturer's own resonances æ (hat), e (men), ei (hay), and i (eat), allowing for variation of pitch due to differences of pronunciation. For the vowel sounds ma, maw, mow, moo, for which Miller finds only a single resonance, observations by ear showed double resonances, one resonance of which in each case was fairly comparable with Miller's single resonance.

It was demonstrated that the English vowel sounds a (calm), e (men), i (eat), ɔ (all), u (who), could be recognisably reproduced by means of an organ reed attached to a single cylindrical resonator of cardboard divided into two resonators of proper pitch by means of a central perforated diaphragm or stop, the actual resonances being a, 1084/683; e, 1722/406; i, 2298/342; 5, 861/483; u, 812/322. The cardboard resonator gave similar vowel sounds to those of plasticene metal or glass.

The same organ reed was attached in succession to two single resonators tuned respectively to Miller's whispered frequencies 781 (ɔ) and 383 (u).

It was shown that though there was a trace of the o sound in the case of a single -resonator of 781, there was no trace of u sound in the case of a single resonator of 383.

Reference was also made to the recent work of Crandall and Sacia (Bell System Telephone Journal, April 1924, vol. 3, No. 2, pp. 232-7). These results of vowel sound analysis made by a system of electrical filters showed clear double resonances for the vowel sounds a, x (not), ou (no), u, U (put), the vowel sound ɔ (all) being shown as having a single extended region of resonance coinciding with that of the two separate resonances heard in the lecturer's voice.

Crandall and Sacia found certain additional resonances. It was suggested that some of these might be distinctive of the American accent. In the lecturer's own voice, when producing the vowel sound æ (hat) with the American accent, an additional resonance of the order of 2,700 was audible. This resonance appeared to be due to a constriction of the pharynx, as though the back resonator were divided into two resonating cavities.

The experiment was shown of constricting a rubber tube model. It appeared that by constriction of the rear portion of the back resonator an appreciable * nasal' quality was added to the vowel sound.

Experiment was shown of slowing down the speed of a dictaphone record of the vowel sound A (as in up) which gave in succession sounds very similar to a (calm), » (not), ǝ (all), and u (who) by successive reduction of the speed of the driving mechanism.

A sound similar to u (put) was also produced by slowing down a record of the vowel sound æ (hat).

The cumulative effect of these experiments appeared to indicate that the vowel sounds a (calm), » (not), ɔ (all), u (who) and u (put) were all in effect due to double

resonance.

The artificial production of consonants by means of resonators was shown, consonants m and n being reproduced by a double resonator of frequency 2169/342 giving the vowel sound I (it) and having a third (nasal) resonator of frequency 704 connected to the back resonator. With this model, closure and release of the mouth during blowing produced mi: closure and release of the central orifice gave ni. The two operations in succession produced the name 'Minnie.'

The production of the consonants p, t, k, v, z, dh, r (untrilled) and r (guttural) was shown by means of a flexible double resonator made of a 1-in. diameter rubber tube actuated by an air-blown reed. It was shown that the different consonants were produced by the varying resonance effects of complete or partial closure and release at different points in the length of the tube. The untrilled r sound was shown to be due to a double constriction.

The consonant sound '1' was proved to be due to a rapid change of resonance, the '1' sound being lost if the same changes were made at a slow speed.

The general conclusion was that the consonant sounds are as essentially musical as the vowels, and are produced in a similar manner, viz.-by resonance.

The

principal differences were that, whereas the vowel sounds represent the effect of different postures of the vocal organs, most of the consonants represent the effect of different gestures or movements by which the successive vowel postures are reached. The consonants were in general produced by resonators of smaller orifice than the vowels, in many cases by more than two resonators, and in many cases by resonances which changed in a characteristic way in pitch or amplitude or both. In general the human ear identifies the characteristic gestures by means of the audible resonance changes which they produce.

11. Prof. P. E. SABINE.-Research in Architectural Acoustics.

A brief summary of the Reverberation or Sound Chamber method of acoustical measurements is presented. This method makes use of the fact that sound from a source within a closed space remains audible for an easily measurable length of time after the source has ceased. This time, T, will depend upon E, the acoustical power of the source, t, the time during which it speaks, V, the volume of air in the room, A, the rate of dissipation of sound energy, and i, the minimum audible sound energy density. Assuming that the time during which the source speaks has been sufficiently great for the density of sound energy in the room to reach the steady state Lo, in which the sound produced per second equals the sound dissipated per second, the time required for the density to fall to the threshold density i is given by the relation

A, for sound of any pitch within a given room, is determined initially by varying the acoustical power of the source of sound in known ratios and measuring the duration of audibility of the residual sound after the source has ceased. A is the slope of the straight line obtained by plotting log E as a function of T. E

Knowing A, the ratio for any observer follows from Equation (1).

The arrangement of the Sound Chamber in the Wallace Clement Sabine Laboratory at Riverbank, Geneva, Illinois, is described. Illustrating the use of such a room, the method and results of a quantitative study of non-musical impact sounds, such as the noise from the operation of typewriters and the like, are given.

The results of a research programme on the general problem of the reduction of sound transmitted by partition walls are summarised. This research has included measurements on so-called sound deadening quilts'; that is, materials which are porous and inelastically compressible and flexible, structural units of wood, glass and steel of various types, and standard masonry partitions of different materials.

The experiments show that reduction of sound in transmission by homogeneous felts and the like is a true absorption process, so that I, the density of sound energy on the further side of a thickness x of a material of this sort, is given by the expression

Thus the sound-insulating value of a material of this character may be specified by the two experimentally determined coefficients r and q.

In masonry walls the resonance of the structure as a whole and in segments is an important factor in sound transmission, so that experiments with a single tone are difficult to interpret. Extending the investigation to the whole scale of tones, experiments on some fifteen different masonry walls of different materials and thicknesses show that the general reduction of sound in transmission through such walls is independent of the material and the structural stiffness of the wall, and is a function only of the weight per unit area.

Friday, August 8.

12. Sir NAPIER SHAW, F.R.S.-If the Earth went Dry.

The phenomena of the general circulation of the atmosphere depend fundamentally upon warming at the surface by the sun's rays and on cooling these by outward radiation, but the dominant factor of weather is the modification due to water-vapour in the air. In this paper, in order to clear ideas, the reader is invited to regard these two aspects of thermal influence as distinct, and to consider the effect of dry heat' alone. We thus form an idea of what the general circulation would be if there were no water-vapour at all in the air. The subject is hypothetical, inasmuch as the actual circulation is generally affected by the condensation or evaporation of water, but its discussion is not necessarily sterile. It is an exercise in some important points of thermal economy; in deserts the conditions postulated are approximately realised, and yet winds, dust-storms, and dust devils' are not infrequent there; and in the large part of the atmosphere where the temperature is below 270 t the relative amount of water-vapour, though not by any means without function, is too small to play the dominant rôle.

It is assumed that dry' air (except for dust) would be perfectly transparent. Radiation received by a perfect absorber normal to the sun's rays would be 135 kilowatts per square dekametre (subject to small variations of the solar constant), and the loss of heat from a surface radiating perfectly (subject to local variation on account of dust) would be .572 × (t/100)4 kw., and range from 9 kilowatts per (10 metre)2 for 200 t to 46 for 300 t. A table is given of the temperatures (between 200 t and 402 t) at which the loss from a radiating surface would balance the income for given solar altitudes.

The technical discussion is in five sections :

1. A survey of the thermal processes operative in the absence of watervapour : (a) the katabatic effect of inclined surfaces cooling in the polar night; (6) the slow thermal convection, upward, by the building up of layers of dry air in convective equilibrium over flat solarised surfaces (incidentally the question of superheated air is dealt with); and (c) the mixing of superposed layers by eddy-motion.

2. An estimate of the flow of air necessary to keep a steady state of temperature on a polar slope under assumed conditions during prolonged nocturnal radiation. A possible value of 300 km. per hour offers a justification for the use of the term 'dust blizzard' as descriptive of the weather.

3. An estimate of 2 km. as the probable daily height of a layer in convective equilibrium under a tropical sun.

4. Diagrammatic sections of surfaces of equal temperature and of equal potential temperature for sunrise and sunset at solstice and equinox. A permanent stratosphere, nibbled daily by a convective troposphere, is presupposed for the purpose of estimating its probable temperature, which is near 300 t. The incidental curiosities of temperature are set out.

5. The pressure and winds consequent upon the temperature are sketched, with the conclusion that a polar front would still be operative and a general circulation not dissimilar in some of its main features from the present form.

13. Sir FREDERIC STUPART.-The Variableness of Canadian Winters.

In normal seasons North Pacific cyclonic areas usually move south-eastward, with their centres well off the coast until at about the latitude of Northern British Columbia they enter the continent, while anticyclonic conditions of moderate intensity with low temperature prevail in Yukon and the Mackenzie River.

In certain years, however, the Pacific cyclonic areas are less intense and enter the continent further south, while great anticyclonic developments occur in the far north and sweep south-eastward over Canada, accompanied by severe cold waves, which not infrequently reach the Atlantic coast. These conditions lead to abnormally cold winters in Canada.

In other years the North Pacific cyclonic areas appear to be of such intensity