Table of contents

1. Measurements of the absorption in aluminium have been made of the X-radiation emitted by an incandescent cathode X-ray tube excited by various forms of high-tension generator. The results show that after traversing 1 cm. of aluminium the coefficient of absorption in aluminium becomes approximately constant.

2. The radiation transmitted through 1 cm. of aluminium is defined as the "end-radiation," and it is shown that for the same value of equivalent spark-gap different machines give different qualities of "end-radiation."

   The induction coil is shown to give different results at the same equivalent spark-gap with different lengths of interrupter contact.

3. Curves showing the observed coefficient of absorption of the "end-radiation" plotted against peak voltage deduced from the equivalent spark-gap are different for different machines, and for the induction coil operated with various lengths of interrupter contact. It is consequently deduced that measurements of equivalent spark-gap do not provide a measure of the hardness of the "end-radiation."

4. The important result is obtained that the absorption curves for the various machines under conditions of the same quality of "end-radiation" are indistinguishable, from which it follows that under these conditions X-radiation is produced in which the intensity distribution in the spectrum is the same for all the machines. Somewhat similar results have been obtained by A. Dauvillier using the X-ray spectrometer. The same result obtains with the induction coil operated with various lengths of interrupter contact.

5. A practical method of measuring the general quality of X-radiation is suggested.

6. The discrepancy between the result obtained with the Wimshurst machine and that obtained by A. Dauvillier with an arrangement producing constant potential led to the suggestion that the output of the former might be of an intermittent character. Experiments are described showing that intermittent X-radiation is produced when the Wimshurst machine is employed as the high-tension generator. A further investigation of this phenomenon is in progress.

The protective values expressed in terms of the equivalent thickness of lead have been measured for a variety of materials. Numerically, 1 mm. of the material in question is equivalent to the following thicknesses of sheet lead in millimetres: -

Lead glass	...	...	...	...	0.12 to 0.20
Lead rubber	...	...	...	...	0.25 to 0.45
Bricks and concrete	...	...	...	About 0.01
Woods	...	...	...	...	...	0.001 or less
Baryta plaster	...	...	...	...	0.05 to 0.13
Steel	...	...	...	...	...	0.15

The above figures relate to tungsten X-rays generated by 100,000 volts.

It is shown that Poisson's method can be readily applied to get the complete solution of the problem of two electrified spherical conductors. The case of a spherical condenser is first considered and simplified methods of computing its capacity are given. Simple expressions for the potentials at the two inverse points due to the charges on each of the spheres are found. Poisson's method is then used to show that the capacity coefficients for two spheres external to one another can be very simply expressed in terms of the capacities of certain spherical condensers and can thus be readily computed in all cases. Formulae for the attraction and repulsion of two electrified spheres are given. When the charges are of like sign the electrostatic energy of the system has a maximum value when the spheres are at a given distance apart. Similarly, when the potentials are of like sign and maintained constant, the electrostatic energy of the system has a minimum value for a definite distance between them. The particular case when the spheres are close together is considered in detail. The exactly analogous problems in thermal and electric conduction are also considered, and it is shown how their solutions can be written down at once. Finally, the formula for the maximum value of the electric stress in the medium surrounding the spheres is given and its practical importance is pointed out. For equal spherical electrodes at a fixed distance apart there is a definite size of radius which makes the disruptive potential difference a maximum. The distance between them where the attraction has a maximum value is also found.

This Paper gives a homographic treatment of the perfect, symmetrical optical instrument; discusses its focal planes, principal planes and nodal points; and shows that these latter are sufficient to define uniquely the optical properties of the instrument.

This Paper deals with the question of the arrangement of the atoms in the molecule of gaseous sulphur dioxide and the manner in which they are linked together. Two suggested arrangements are considered in detail, and evidence is brought forward, based on the determination of molecular dimensions as derived from viscosity measurements, which suggests that the more probable arrangement is that in which chemical bonds exist between each pair of the three atoms, i.e. two S-O bonds and one O-O bond.

This Paper relates to the heating of rubber when suddenly immersed in various vapours. It describes the method of measuring the thermal changes by means of thermoelectric junctions and gives the results obtained with benzene, pyridine, ammonia and water-vapour. The effect is compared to that of water-vapour on cellulose.

The various theories of the action of the Singing Flame put forward since its discovery are reviewed, and experiments to test the relative merits of the two most recent theories are described; Lord Rayleigh's theory is shown to fit the results most closely, in that (1) heat is given by the flame to the air in the tube at each condensation, and (2) stationary waves are formed in the gas as well as in the air-tube. But the lengths of gas-tube unfavourable to the "singing" cover, in fact, a much more restricted range than Lord Rayleigh surmised.

A number of rays in an axial plane (and a few general rays) are traced through the lens systems by exact methods, and on each ray the positions of the conjugate points for unit magnification are found by Mr. T. Smith's formulae. The results show that for general rays the loci of these "unit points" are three-dimensional. The loci are surfaces only when the chief rays are bound by some conditions, such as passing through a fixed point of the object. In this case the unit surfaces are not fixed, but shift with the object point. The curvature changes with aperture, and with the distance of the object point from the optic axis. Hence the unit surfaces cannot coincide with wave-fronts. Within the region for which the lenses are designed, the curvature of both object and image unit-point loci is positive (convex to the light source) and the image locus is more curved than the object locus. These facts do not coincide with the theoretical conclusions obtained by Mr. Smith for either a thin system or an ideal thick system, but accord more nearly with the latter, especially as regards the sign of the difference of curvatures of the two unit surfaces.

In the theory of the vibration galvanometer with one degree of freedom certain specified conditions are assumed to hold. If these conditions are not satisfied in a galvanometer, the instrument will show multiple resonance. This indicates the need of a more general theory. The theory of vibrations of a system with two degrees of freedom is briefly given, expressions for the amplitudes of the forced vibrations are deduced, and the conditions for resonance ascertained. The results are applied to a galvanometer in which the moving system is asymmetrically hung on a laterally yielding axis, and it is shown that the formula for the amplitude is capable of reproducing with fair accuracy the sensitivity curve of the galvanometer, which shows multiple resonance. Asymmetry always lowers the sensitivity of the resonance, and the loss can be ascertained by the help of the sensitivity curve. The analogy to the vibrations in coupled circuits is pointed out.

I wish to express my gratitude to A. Campbell for helpful criticism, advice and references.

The methods of X-ray analysis enable the number of molecules associated with the unit cell to be determined. With the help of this information an attempt is made to connect the symmetry properties of the crystal with this number and with the symmetry properties of the molecules from which the crystal is formed.

The symmetry number for each of the 32 crystal classes is given, and is shown to mean the minimum number of asymmetric molecules necessary in the unit cell to satisfy the symmetry conditions. The relative orientations and positions of these molecules in the cell are discussed.

It is suggested that this symmetry number is the actual number of molecules in the cell when the molecule is asymmetric; further that, if the molecule possesses symmetry, this symmetry appears also in the crystal, and the number of molecules in the unit cell is obtained by dividing the symmetry number of the crystal by the symmetry number of the molecule.

Evidence is produced in support of these hypotheses and examples are given of their application to inorganic and organic crystals

Plates of aluminium, iron, copper, lead and magnesium have been examined by means of the Bragg X-ray spectrometer employing radiation direct from a molybdenum anti-cathode. The maxima observed in the spectra are sufficiently intense to measure with accuracy, and the crystalline structure of the materials examined are readily determined. A few of the results obtained by the method are included in the Paper as typical examples.

The Paper deals with a new form of cathode-ray oscillograph adapted for commercial production and laboratory use. The instrument described is of the low-voltage type, in which a hot cathode is employed as a source of the electron current. This low-voltage type of oscillograph is much more sensitive than the high-voltage cold cathode type designed by M. Dufour. Various methods are described for focusing the cathode-ray stream, and a proposal has been made for an oscillograph with external (i.e., outside the vacuum) photographic film. Experiments have been made to determine the most suitable photographic film or plate. Ordinary gelatine coated roll films or plates are unsuitable, owing to the marked absorption of the cathode-rays by the gelatine. The best results have been obtained with Schumann plates containing a proportion of calcium tungstate. This material phosphoresces with a light rich in ultra-violet, and consequently the secondary luminous effect on the Schumann plate is very great.

Mechanical, electrostatic and electromagnetic methods are described for generating a time-axis on the records. For certain purposes this time axis is sinusoidal, whilst for others it is linear. Numerous records of high-frequency A.C. wave forms and of impulsive electrical phenomena have been obtained, and a few of these are reproduced in the Paper. Brief reference is made in conclusion to the applications of the oscillograph to research and electrical engineering problems, where other well-known forms of oscillograph (Duddell, Einthoven, &c., types) cannot be employed on account of the inertia of the moving element.

In a recent Paper in Terrestrial Magnetism, Dr. L A Bauer draws the conclusion that both the range of the diurnal inequality of atmospheric electricity potential gradient and the mean value of the element for the year increase and diminish with sunspot frequency. This conclusion was based on observational data from the Ebro Observatory, Tortosa, Spain, between 1910 and 1920.

The present Paper investigates the subject more mathematically, employing Kew electrical data from two periods of years, in addition to the Ebro data utilised by Dr. Bauer. Magnetic data from Kew Observatory for the same periods are similarly treated, so as to have parallel results from an element for which the sunspot relationship is generally admitted.

The results obtained are on the whole not incompatible with Dr. Bauer's conclusion, but they indicate that if a relationship of the kind supposed exists, the sunspot influence must be very much less in the case of atmospheric electricity than in that of terrestrial magnetism.

The Paper relates to a further improvement in the pump recently described in the Proceedings of the Society, which is designed to avoid irregularities due to air skins on the inner surfaces of the apparatus. The present improvement consists in means for providing a mercury seal during periods when the pump is out of use, whereby the formation of fresh air skins is prevented.

Zero methods are proposed, and expressions derived, for the measurement of power factor and effective resistance of alternating current loads. The methods are extended to high tension circuits.

The effect of "electrical control" of the needle of the quadrant electrometer is discussed, and it is shown that the usual formula for the instrument is applicable only when the needle is maintained at its mechanical and electrical zero. The further advantages of null methods are emphasised.

Illustrative tests are recorded.

The Eötvös Gravity Balance in the Science Museum, South Kensington, is described, and the theory of its operation considered. A full account is given of certain preliminary experiments made on the torsion wires, with a view to ascertaining the daily variation of the equilibrium position, due to strains set up in the wires during manufacture. Until this daily shift has been eliminated the instrument cannot be employed successfully. The experiments show that a preliminary treatment of the wires is desirable, and a test was also made of the "baking" method recommended by Eötvös for ageing the wires. This method was found to give the desired result, and after this treatment the reading of the instrument remained practically constant from day to day.

Tables are given showing the variation in the reading of the instrument when its beam is rotated into different azimuths, and the constancy of these readings when repeated. The differences in the readings as the azimuth varies are sufficiently marked to indicate the changes in the local gravitational field of the laboratory, and further experiments are being carried out to determine these changes in detail, as a preliminary to field tests; it is hoped to communicate the results of these experiments at a later date.

The author in an address recently published put forward evidence for regarding the benzene ring as an actual structure of ascertainable size and form, and deduced that the unit cells of naphthalene and anthracene should have two of their axes equal, the third axis being longer for anthracene than for naphthalene by the width of one ring. The experimental data then available supported this hypothesis only roughly; in the present Paper it is shown that more reliable data, subsequently obtained from small but perfect anthracene crystals, agree with it very closely. It is pointed out that the X-ray data furnish a new and accurate method of determining the density of a crystal.

The Paper describes measurements of the natural frequency of diaphragms of various sizes having a rigid rim and a central boss for attachment of a microphone or receiver. In air the frequency was found by means of a monochord, but under water the resonance-frequency was noted in the neighbourhood of a subaqueous transmitter of variable pitch. The results are in good agreement with the theoretical conclusions of Prof. H. Lamb. In many cases harmonies were observed round about a fifth or an octave above the fundamental, but their occurrence was capricious, and their pitch inconsistent with theory. The resonance peaks of the frequency curves are more or less of the same area, being high and narrow or low and broad.

The effect of increasing the pressure on one side of the diaphragm was studied, and the pressure-displacement curve was found to be linear up to the elastic limit, while the pressure-frequency curve is of the saturation type. A large diaphragm is less affected by pressure (and therefore by iminersion in deep water) than a small one of the same natural frequency, in consequence of its greater thickness.

A description is given of a series of experiments carried out to test the possibilities of the Radio-Acoustic method as a means of locating positions at sea. In this method as applied to navigation, for example, the ship requiring her position makes a W/T "dash" at the same instant as a small charge is fired in the sea. A station on shore records the arrival of the W/T signal and also of the explosion wave at a number of hydrophones suitably disposed in known positions on the sea-bed. The times of travel of the explosion wave, and hence the distances from the charge to each hydrophone, are indicated by an Einthoven galvanometer photographic recorder.

The method permits of great accuracy and has important applications in navigation and hydrographical survey. For navigational purposes great accuracy is sacrificed to speed - it being possible to give a ship her position within a radius of half a mile within 10 minutes of receiving her request for a location. A 9 oz. charge of explosive can be located at 40 miles. In hydrographical survey work the method has already been used successfully in fixing accurately the positions of certain buoys and light vessels.

The possibility of screening and distortion effects produced by sandbanks has been investigated.

The radio-acoustic method has been thoroughly tested under working conditions. It has proved accurate and reliable by day or night in rough or in foggy weather and at all seasons of the year. Many locations have been given by the method and no failures have been experienced.

The R/A system should be regarded as a serious competitor to the method of location by directional wireless.

In order to distinguish bubbles generated by chemical action in glass from those introduced by mechanical processes spectroscopic tests are made for the presence of nitrogen. In order to liberate the gas from the bubbles a specimen of the glass is placed in one limb of a quartz U-tube and mercury in the other, and the glass is heated and then disintegrated by sudden cooling, the tube being plunged into cold water at the same time that the mercury is thrown on to the glass.

The Paper deals with the difficulties arising from residual traces of air fouling the vacuum above the mercury column in syphon gauges and other devices. A remedy is suggested in the form of a small attachment taking the shape of bent capillary tubing ending in a bulb. This enables the air to be repeatedly pushed into the vacuum of this bulb, the mercury at the bottom of the capillary preventing the subsequent return of the air. With such an arrangement fitted to the top of a syphon gauge the height of the column of mercury becomes a true measure of the gas pressure, subject only to the definite correction for the vapour pressure of mercury and temperature. The device is regenerative in the sense that, irrespective of any progressive fouling of the vacuum, a fresh air-free vacuum is automatically created by it every time it is brought into action. As typical examples of the wide field of utility of the device its application to mercury barometers and mercury vapour lamps is also briefly discussed.

In a Paper read before this Society on February 9, the Eötvös Torsion Balance was described in detail, and the theory of its operation considered, the preparation of suitable torsion wires was mentioned, but no practical tests with the instrument were discussed.

In view of the sensitivity of the balance, which, as previously stated, measures derivatives of gravity of the order of 10^-9 C.G.S. units, it was anticipated that a gravitational survey of the laboratory would disclose the varying effects of the neighbouring masses of the walls, pillars, &c. The balance was therefore set up at different stations in the laboratory, and the derivatives at each station measured. The measurements at several stations were checked by repetition, and the results compared with the theoretical values.

The mutual consistency of the results obtained at each station, and their general agreement with the calculated effects exceeded expectations, as the local gravitational field varied so rapidly that the theoretical assumption of a uniformly varying field in the neighbourhood of a station was obviously vitiated.

A method is described which enables the effect on the thermal conductivity of a wire of twisting the wire to be measured. In each of the steel, aluminium, copper and lead wires tested the twist decreases the conductivity along the wire by a small amount which is approximately proportional to the square of the twist per unit length.

The change of electrical conductivity is found to be in general less than the change of thermal conductivity, but it is also approximately proportional to the square of the twist per unit length.

In the preliminary section, the loss angle of an imperfect condenser is defined, the equations for the Wien bridge are derived, and the effects of variations of frequency and voltage on the balance are discussed.

One of the difficulties in the application of large potential differences to a bridge is the effect on the arm which has to withstand the high voltage. In the arrangements due to Monasch and Schering, this arm is the known condenser; in the bridge as used by the author, the voltage is applied to the ratio coils. The errors introduced by earth impedance are eliminated by using the Wagner auxiliary bridge.

The applications to measurements on cables are considered, and the use of the double bridge in determining the "wire-to-wire" and "wire-to-sheath" losses in a multi-core cable is described.

In Appendix I. the corrections due to imperfections of the bridge arms are discussed, and in Appendix II. a simple quantitative theory of the double bridge is given.

The galvanometer is designed to secure rapid indication and steadiness of reading without unduly sacrificing the sensibility. The coil is long and narrow, and therefore of small moment of inertia: the mirror is supported by the wires forming the coil, between which it is slipped, and the coil is supported between an upper and a lower vertical wire, as distinct from strips, made of silicium bronze and put in tension.

The thermopile is designed to be quick-reading and free from zero-errors, as well as sensitive. The cold junctions are in contact with metal masses which keep down their temperature, and in order that the hot junctions may have small heat capacity the bi-metallic strips composing the thermopile are made of plates of constantan and manganine silver-soldered along an edge, rolled in a direction parallel to the edge into thin foil, and then cut into strips perpendicular to the edge.

X-ray photographs of certain sodium salts of the fatty acids (soap curds) show lines due to reflections from planes with very wide spacings of the order 40 A.U. These planar spacing increase uniformly with the number of CH₂ groups in the molecule, indicating an effective length of 1.25 A.U. for the CH₂ group. These and other lines can be accounted for by assuming that the curds are in the smectic state described by Friedel.