Table of contents

Correction to Proc. Phys. Soc.47 471

Correction to Proc. Phys. Soc.47 777

Measurements of wave-lengths have been made by interferometer and hot-wire methods, and of absorption by hot-wire methods alone, for supersonic radiation at frequencies between 40 and 2000 kc./sec. in carbon dioxide, nitrous oxide and sulphur dioxide at various pressures up to two atmospheres. For the hot-wire method, a circuit which gives a linear relation between amplitude or particle velocity and response at constant frequency is described. The velocity-measurements in the former two gases may be reduced to a common curve by plotting them against the parameter {frequency/pressure}; although the observed rise in velocity in the region where this parameter lies between 100 and 1000 is in accordance with the relaxation-time theory, the decrease in velocity at lower and higher values is not. In sulphur dioxide the rise of velocity is in the neighbourhood of 4000. The absorption in all three gases rises sharply at pressures below 400 mm. of mercury.

Measurements of wave-lengths of supersonic radiation at frequencies between 40 and 140 kilocycles per sec. have been made in carbon dioxide, nitrous oxide and sulphur dioxide at various temperatures from room-temperature up to 200°C. The velocities at constant density, i.e. reduced to 0°C., have been calculated. When these are plotted against temperature, supersonic dispersion is shown by a sharp fall of velocity in carbon dioxide at a temperature which increases with the frequency of the source. The significance of these results in the light of the theories of supersonic dispersion which have been propounded is then discussed.

The direct impact of two cylindrical jets of liquid causes the liquid to emerge radially in a plane at right angles to the common axis of the jets. The maximum diameter of the disc of moving liquid so formed is shown to depend on the surface tension of the liquid.

A method of measuring surface tension is developed and is applied to measure the surface tension of water, giving 73.8₃±0.1₃ dyne/cm. at 15°C.

The liquid surface is renewed about 80 times per second, contamination being thus prevented. The only other method in which such rapid renewal of the surface takes place is the Rayleigh oscillating-jet method. The angle of contact is not involved in Rayleigh's method, nor in the present method.

Measurements on the paramagnetic susceptibility of cerium chloride CeCl₃.6H₂O in aqueous solutions have been made over a wide range of concentrations (8 to 37.5 per cent of the anhydrous salt) and for the temperature-interval 7° to 70° C. by means of a slightly modified Quincke ascension method. The variation of the molecular susceptibility with temperature is found to follow, for the interval considered, a Curie-Weiss law χ_c (T+Δ)=C, with C equal to 0.762.

The value of C appears to be unaffected by the variation of the concentration of the solution. On the other hand, Δ varies with the number of ions present in the unit of volume and increases from 45 to 63 for the range of concentration considered.

The effective magneton number μ_e or 14.07 (χ_cT)^1/2 of the ion Ce⁺⁺⁺ at room temperature is calculated and is found to vary, for this same interval of concentrations, from 11.41 to 11.16. If, on the other hand, the magneton number is deduced from the modified form of the above formula, μ_w=14.07{χ_c (T+Δ)}^1/2, a value is obtained which is independent of the concentration and of the temperature and is equal to 12.36.

These results are compared with the values obtained experimentally by other workers and with the theoretical numbers deduced by Hund and Van Vleck from the study of the spectroscopic ground states of the rare-earths group.

Some measurements on the densities of the solutions under investigation are included.

The magnetic susceptibilities and electrical conductivities of cobalt, nickel and palladium and of their alloys with copper, silver and gold are discussed on the basis of the quantum theory of metals. It is shown that the number of electrons in the outermost s state must be about 0.6 per atom in the transition metals and one in the noble metals; certain magnetic properties of the alloys are explained on the basis of this fact. A quantum-mechanical explanation of the relatively high resistance of the transition metals is given and is shown to be supported by measurements of the resistance of alloys.

The present memorandum discusses methods of determining the electrical resistivity of the earth, particularly from the point of view of the correlation of a.-c. and d.-c. methods. Various experimental methods are discussed together with the theory of current flow in homogeneous and stratified media. The topics considered are illustrated from experiments made to confirm the Carson-Pollaczek formulae for alternating currents in the earth and from surveys made from time to time in connexion with the problem of telephone interference. Various alternative methods are recommended for use in different circumstances.

The fundamental problems in the direct measurement of the Peltier coefficient are discussed with reference to the various methods available. A new apparatus is described which includes all-metal calorimeters, separate from the specimens, and a differential platinum resistance thermometer. With a sufficiently good thermostat this would just detect a steady heating of the order of 10^-7 cal./sec. The high sensitivity of this arrangement has permitted a strict test of the proportionality of the Peltier effect to current to be carried down to 0.012 A., with copper-constantan junctions. The error due to thermal losses along the leads has been especially studied, and estimates of the loss have been made.

The relative merits of plane- and concave-grating spectrographs for precise measurement of wave-length between 10 and 100 A. are discussed. It is shown that experimental conditions do not allow full advantage to be taken of the superior resolving-power of the concave grating. A plane-grating spectrograph was designed for relative wave-length measurements of high precision; its dispersion and resolving-power are calculated, and a number of wave-length determinations relative to Cu Lα₁₂, viz. 13.310 A., are reported. Microphotometer curves of the K line of carbon show that this line has, besides the principal line, two components of shorter wave-length. This result is in good accordance with that of other workers.

Owing to the use of acoustical outputs up to 500 watts in modern public-address loud-speaking apparatus, it is necessary to consider the distortion due (mainly) to the adiabatic pressure-volume relationship for air being non-linear. The physical principles underlying the transmission of sound-waves of finite amplitude in expanding waves are epitomized, and the differential equation for a horn of any cross-section is stated. The equation is solved for spherical-wave propagation, which includes the case of a conical horn having any solid angle up to 4π. Formulae are given which enable the shapes of the particle amplitude and pressure waves to be calculated to a second approximation. As the sound travels down the horn, the crests of the waves tend to overtake the troughs, and harmonics are created, the power associated therewith being transferred from the fundamental. The ratio of the power in the second harmonic to that in the fundamental is obtained, and comparison made with that for a uniform tube and an exponential horn. The analysis is illustrated by numerical examples, and design formulae are deduced from which the area of the horn-throat to keep the distortion below a prescribed limit can be calculated. Lamb's analysis for a uniform tube has been extended from the second to the third approximation.

The viscosity of aqueous solutions of potassium chloride and of potassium sulphate has been measured over a wide range of temperature. Every care has been taken to eliminate, or to correct for, sources of error. The results have been analysed by plotting (ϕ/ϕ₀ - I)/√c against √c, and in those cases where the relation between these variables proved to be linear the values of A and B in the equation

ϕ/ϕ₀ = I + A√c + Bc

at each temperature have been calculated.

Analyses of arcs between plain soot carbons of various degrees of purity were carried out with a quartz spectrograph. The normal vertical two-electrode arc and also a horizontal three-electrode arc of Y form, with two negative carbons and one positive, were used, parts of the arc flame only being photographed. The object was to find a correlation between the spectra and the candle-power per ampere of the positive crater of the three-electrode arc. The effects on the spectra of the following changes in conditions are given: (i) changing the positive carbon while keeping the negative carbons the same; (ii) special purification of the carbons; (iii) sputtering of the arc; (iv) photographing different parts of the arc (a) close to the positive carbon, (b) centre of the arc flame, (c) close to the negative carbons. Photographic enlargements of the ultra-violet parts of the spectra are given.

Descriptions of some experiments to liquefy hydrogen by the expansion method (a) by pure expansion, and (b) by the additional use of the Joule-Thomson effect. The yields are of such an order that it seems promising to build large hydrogen-liquefiers on this principle.

The humidity corresponding to various wet-and-dry-bulb temperatures between -2° C. and -19° C. has been measured. The wet-bulb temperatures were obtained by means of mercury thermometers, thermocouples and resistance thermometers, all three methods agreeing well.

The actual humidity was generally obtained from a specially designed dew-point apparatus, thermojunctions being used to measure the temperature of the metal surface on which the deposit of dew was formed. In addition, tests by the gravimetric method were carried out.

The results are utilized to prepare a table giving the relative humidity at various wet-and-dry-bulb temperatures. These agree, for the most part, with previous tables, but they differ in the region of low dry-bulb temperatures (below about -9° C.) and small wet-bulb depressions (less than 1° C.).

The results are also examined from the point of view of the usual theory which asserts that (e'−e) = B₀P (θ − θ'), where e' is the saturation vapour pressure at the wet-bulb temperature θ', e the saturation vapour pressure at the dew point (i.e. the actual partial pressure of water in the air), θ the dry-bulb temperature, P the barometric pressure and B₀ the psychrometric constant. Although above 0° C. this formula is found to hold well, yet below 0° C. it is found that B₀ varies in a complicated manner with the temperatures. It tends to infinity when the wet-bulb depression tends to zero, and there is a further variation superimposed on this one; at a constant value of the depression, B₀ passes through a minimum and then through a maximum as the dry-bulb temperature decreases.

The vortices produced by sound in jets of air are examined by stroboscopic cinematography, and their velocity, growth, and angular velocity are determined. It is found possible to explain the salient characteristics exhibited by sensitive jets and the mechanism of their sensitivity. The physical processes underlying the instability of gaseous jets in general are discussed also.

Experimental methods are described for the production of single crystals of tin and for the determination of their orientations by optical measurements. The conditions under which parts of the crystals can be caused to twin by impact or by tension are investigated, and the determination of the energy relations for certain controlled cases is described. It is found that when twinning occurs, energy amounting to 8 × 10⁵ ergs is converted into heat per cm³. of crystal twinned. The process of twinning in relation to the crystal structure of tin is discussed.

The coincidence experiments of Bothe-Kolhörster, Rossi and others, considered in the light of various alternative interpretations, show the existence of penetrating, electrically charged particles which are either primary cosmic rays or are secondaries of primaries that are absorbed high in the atmosphere. The shower-producing radiation, which seems to consist of photons, must, in view of the marked latitude effect to which it is subject, be produced by some electrically charged primary rays, which are provisionally identified as electrons.

The variation of cosmic-ray-intensity with latitude is shown to increase from about 16 per cent at sea-level to a ratio of 40-fold between 55° and 20° at very high altitudes. Extrapolation to the top of the atmosphere near the poles and the equator would indicate a ratio greater than 100: 1, which would imply that less than 1 per cent of the unfiltered primary cosmic rays are electrically neutral. In conjunction with the coincidence experiments, this means that the primary rays responsible for cosmic-ray effects are nearly all electrically charged particles.

A method of analysing these electrically charged rays is described and applied to typical ionization data for different altitudes at various latitudes. The method consists in (1) calculating the effective minimum energy of various types of particles admitted through the earth's field at different magnetic latitudes; (ii) determining the minimum ranges in air of the particles corresponding to these minimum energies; and (iii) analyzing the data relating the altitude with ionization and thus obtaining experimental range-minima that can be compared with the calculated values. The balloon experiments show two such range-minima, A and B, at higher and lower altitudes respectively. Their ranges progress with changing latitude approximately in the manner that the theory predicts. A third range-group C appears on analysis of the curve showing the latitude effect for sea-level. Using the best available information regarding magnetic latitudes and the relation between energy and range, these range-groups are identified respectively as alpha particles, electrons and protons. Comparison with directional experiments indicates that the electron group probably consists of about equal parts of positrons and negatrons.

The possible errors involved in applying this analysis are of such magnitude as to leave the identification of the range-groups questionable. Comparison with other data is on the whole however confirmatory, except for the failure to find proton tracks in Wilson photographs of cosmic rays. For this a possible explanation is offered.