way. The scheme will, of course, also be beneficial to the company, but it will be much more useful to the workers, not only directly, but also by inculcating among them the thrift habit, which, if duly learned and assiduously practised, will enable the workers to look forward to the future with greater confidence than if they were mere wage-earners, without any further interest in th welfare of the business from which they in the welfare of the business from which they get their living. The promoters of beneficent schemes of this kind are the real friends of the working classes, and they are also doing their part in promoting peace in industry and the general welfare of the whole community. Proceedings and Notices of Societies. THE ROYAL SOCIETY. The following papers were read at the meeting held on Thursday, January 26:- The Formation of Crystals of B-Brass. By G. I. TAYLOR, F.R.S. a It is shown that B-brass, which has crystal structure similar to that of old iron, behaves in a similar, though not identical, manner when distorted. The peculiar feature of the distortion of iron crystals, namely, the fact that slip does not occur on a definite crystallographic plane, is repeated in ẞ-brass within a certain range of orientations of the crystal axes in the specimen. On the other hand, in another range of orientations slip occurs on a definite crystal plane of type (110). The conditions which determine which of these types of distortion will occur in any given case are investigated, and it is shown that the determining cause is the variation in resistance to shear which occurs as the plane of slip rotates about the direction of slip. This variation is calculated from the experimental results within the range to which they apply, and it is shown that resistance to shear is least when the plane of slip coincides with a crystal plane of type (110). On either side of this position shear stress increases linearly, there being a discontinuity in the rate of change of shear strength with orientation of plane of slip. This peculiar property is also possessed by the model consisting of hexagonal rods proposed by the author and Miss Elam, and by Mr. Hume Rothery's models, which, from this point of view, is identical with the model of hexagonal rods. It is shown also that in ẞ-brass resistance to slipping in one direction on a given plane of slip is not the same as resistance offered to slipping in opposite direction. Such a difference is to be expected from crystallographic symmetry, but was not observed in a-iron. The Behaviour of a Single Crystal of a-Iron Subjected to Alternating Torsional Stresses. By H. GOUGH. Communicated by T. E. Stanton, F.R.S. A single crystal of a-iron has been subjested to various ranges of alternating torsional stresses, leading to elastic and total failure. Changes in microstructure, and method of failure in relation to crystallograhic structure and to the stressing system, have been studied by mechanical, microscopical and X-ray methods. The results indicate that direction of slip coincides with that of most highly stressed principal line of atoms. Four such possible directions of slip exist within the crystal, each being parallel to the normal to one of the four sets of octahedral planes, and at any point on circumference of crysta there exists a plane on which the value of shear stress on the plane resolved in one of the octahedral directions is a maximum. In the general case, this plane of maximum resolved shear stress is not a crystallographic plane of low indices, and slip will only occur on this plane if the latter happens to coincide with a dodecahedral (110), icositetrahedral (112) or hexakis-octahedral (123) plane; also deformation occurs by slip on two crystallographic planes, each plane belonging to one of these three types. These slip planes are not both of one crystallographic type and are situated on opposite sides of the plane of actual maximum resolved shear stress, being determined by the fact that each slip plane is subjected to a greater value of resolved shear stress than any other available slip plane situated on the same side of the plane of maximum resolved shear stress. Owing to the geometry of the structure under these conditions, slip only occurs on one of the following two combinations of planes : THE PHYSICAL SOCIETY. Friday, December 9, 1927, at the Imperial College of Science. Prof. D. W. Richardson, M.A., D.Sc., F.R.S., in the chair. Percy Wilson, M.A., was elected a Fellow of the Society. The President announced that the Council had elected Robert William Sutton a Student Member of the Society. The following papers were read : The Scattering of Light by Individual Particles in Smokes. By H. P. WALMSLEY. Applying the expression given by Maxwell for the number of collisions that occur between two sets of spherical uncharged molecules in a gas to the case of a smoke whose particles cover a wide range of sizes, it appears that particles of a given set collide less frequently with themselves than with those in sets of much larger or much smaller size. If the particles unite on contact, one would expect therefore that the units of the resulting aggregates would differ greatly in size. As this result is at cariance with the deductions of Patterson and Whytlaw Gray from experimental data, the validity of their argument is discussed. On the Construction and Standardisation of an Interferometer Pressure Gauge. By J. J. MANLEY, M.A., Research Fellow, Magdalen College, Oxford. This paper deals with the application of a Michelson interferometer to the determination of gas pressures ranging from 0.0001 to 20 mm. of mercury. The construction of the instrument is fully described as are also the methods used for standardising the registering micrometer screw and its graduated head. The gauge can be instantaneously set and the pressure which obtained. at the moment of setting measured at leisure. The Dielectric Constant of Liquid Bromine. By ANNE I. ANDERSON, B.Sc. An account is given of a re-determination of the dielectric constant of liquid bromine, the value found being 3.199 at 15° C., and at a frequency of 187,000 per sec., with a temperature coefficient of 0.00191 referred to 0° C. Applying the dipole theory of Debye and Gans to the results, a value of 0.40 × 10-18 is deduced for the electric moment of the bromine molecule Br2. The electrical conductivity was also measured. MINERALOGICAL SOCIETY. The following papers were read at the meeting held on January 10, Dr. G. T. Prior, F.R.S., President, in the chair : Potarite, a New Mineral Discovered by the late Sir John Harrison in British Guiana. By DR. L. J. SPENCER. Small nuggets and grains of a brittle white metal have been found very sparingly by diamond-washers in the neighbourhood of the Kaieteur Falls on the Potaro River. This mineral, previously erroneously described as "allopalladium," was proved by Harrison to be a compound of palladium and mercury, PdHg, with a density (15.016.1) considerably higher than that of either of theh component metals. There is a crystalline structure which on the surface of one nugget is shown as indistinct cubic octahedra. The original "allopalladium" from the Harz Mts., supposed to be a hexagonal modification of palladium, could not be procured for a re-examination; it is probably the ordinary cubic palladium. A Simple and Accurate Constant-Volume Pyrometer for Specific gravity Determination. By DR. H. V. ELLSWORTH. The pyrometer of 10 c.c. capacity is made of silica-glass, thus possessing several advantages over one made of ordinary glass. The stopper is perforated by a capillary and is continued into a graduated side-tube, which dips under water while the apparatus is cooling. The volume of the contained water to the graduations on the side-tube can be readily and accurately determined to 0.00002 c.c. The Optical Orientation of Labradorite from County Down (Ireland), Determined by the Fedorov Method. By W. CAMPBELL SMITH. The labradorite from basaltic dikes at St. John's Point, Ardglass, Co. Down, of which the chemical composition and refractive indices were published in 1912 has been studied by the Fedorov method and the optical orientation determined. Dr. C. E. Tilley demonstrated the inversion of CaSiO, in a metamorphic limestone from Larne, Co. Antrim (Ireland); and Mr. A. F. Hallimond exhibited an electromagnetic separator for mineral powders. GEOLOGICAL SOCIETY OF LONDON. The following communication was read at the meeting held on January 11, 1928 : The Geology of South-Eastern Arabia. By GEORGE MARTIN LEES, M.C., D.F.C., F.G.S. way. The scheme will, of course, also be beneficial to the company, but it will be much more useful to the workers, not only directly, but also by inculcating among them the thrift habit, which, if duly learned and assiduously practised, will enable the workers to look forward to the future with greater confidence than if they were mere wage-earners, without any further interest in th welfare of the business from which they in the welfare of the business from which they get their living. The promoters of beneficent schemes of this kind are the real friends of the working classes, and they are also doing their part in promoting peace in industry and the general welfare of the whole community. Proceedings and Notices of Societies. THE ROYAL SOCIETY. The following papers were read at the meeting held on Thursday, January 26 : The Formation of Crystals of B-Brass. By G. I. TAYLOR, F.R.S. It is shown that ẞ-brass, which has a crystal structure similar to that of old iron, behaves in a similar, though not identical, manner when distorted. The peculiar feature of the distortion of iron crystals, namely, the fact that slip does not occur on a definite crystallographic plane, is repeated in ẞ-brass within a certain range of orientations of the crystal axes in the specimen. On the other hand, in another range of orientations slip occurs on a definite crystal plane of type (110). The conditions which determine which of these types of distortion will occur in any given case are investigated, and it is shown that the determining cause is the variation in resistance to shear which occurs as the plane of slip rotates about the direction of slip. This variation is calculated from the experimental results within the range to which they apply, and it is shown that resistance to shear is least when the plane of slip coincides with a crystal plane of type {110}. On either side of this position shear stress increases linearly, there being a discontinuity in the rate of change of shear strength with orientation of plane of slip. This peculiar property is also possessed by the model consisting of hexagonal rods proposed by the author and Miss Elam, and by Mr. Hume Rothery's models, which, from this point of view, is identical with the model of hexagonal rods. It is shown also that in ẞ-brass resistance to slipping in one direction on a given plane of slip is not the same as resistance offered to slipping in opposite direction. Such a difference is to be expected from crystallographic symmetry, but was not observed in a-iron. The Behaviour of a Single Crystal of a-Iron Subjected to Alternating Torsiona! Stresses. By H. GOUGH. Communicated by T. E. Stanton, F.R.S. A single crystal of a-iron has been subjested to various ranges of alternating torsional stresses, leading to elastic and total failure. Changes in microstructure, and method of failure in relation to crystallograhic structure and to the stressing system, have been studied by mechanical, microscopical and X-ray methods. The results indicate that direction of slip coincides with that of most highly stressed principal line of atoms. Four such possible directions of slip exist within the crystal, each being parallel to the normal to one of the four sets of octahedral planes, and at any point on circumference of crysta Ithere exists a plane on which the value of shear stress on the plane resolved in one of the octahedral directions is a maximum. In the general case, this plane of maximum resolved shear stress is not a crystallographic plane of low indices, and slip will only occur on this plane if the latter happens to coincide with a dodecahedral (110), icositetrahedral (112) or hexakis-octahedral (123) plane; also deformation occurs by slip on two crystallographic planes, each plane belonging to one of these three types. These slip planes are not both of one crystallographic type and are situated on opposite sides of the plane of actual maximum resolved shear stress, being determined by the fact that each slip plane is subjected to a greater value of resolved shear stress than any other available slip plane situated on the same side of the plane of maximum resolved shear stress. Owing to the geometry of the structure under these conditions, slip only occurs on one of the following two combinations of planes : The Scattering of Light by Individual Particles in Smokes. By H. P. WALMSLEY. Applying the expression given by Maxwell for the number of collisions that occur between two sets of spherical uncharged molecules in a gas to the case of a smoke whose particles cover a wide range of sizes, it appears that particles of a given set collide less frequently with themselves than with those in sets of much larger or much smaller size. If the particles unite on contact, one would expect therefore that the units of the resulting aggregates would differ greatly in size. As this result is at cariance with the deductions of Patterson and Whytlaw Gray from experimental data, the validity of their argument is discussed. On the Construction and Standardisation of an Interferometer Pressure Gauge. By J. J. MANLEY, M.A., Research Fellow, Magdalen College, Oxford. This paper deals with the application of a Michelson interferometer to the determination of gas pressures ranging from 0.0001 to 20 mm. of mercury. The construction of the instrument is fully described as are also the methods used for standardising the registering micrometer screw and its graduated head. The gauge can be instantaneously set and the pressure which obtained at the moment of setting measured at leisure. The Dielectric Constant of Liquid Bromine. By ANNE I. ANDERSON, B.Sc. An account is given of a re-determination of the dielectric constant of liquid bromine, the value found being 3.199 at 15° C., and at a frequency of 187,000 per sec., with a temperature coefficient of 0.00191 referred to 0° C. Applying the dipole theory of Debye and Gans to the results, a value of 0.40 × 10-18 is deduced for the electric moment of the bromine molecule Br. The electrical conductivity was also measured. - MINERALOGICAL SOCIETY. The following papers were read at the meeting held on January 10, Dr. G. T. Prior, F.R.S., President, in the chair : Potarite, a New Mineral Discovered by the late Sir John Harrison in British Guiana. By DR. L. J. SPENCER. Small nuggets and grains of a brittle. white metal have been found very sparingly by diamond-washers in the neighbourhood of the Kaieteur Falls on the Potaro River. This mineral, previously erroneously described as "allopalladium," was proved by Harrison to be a compound of palladium and mercury, PdHg, with a density (15.016.1) considerably higher than that of either of theh component metals. There is a crys talline structure which on the surface of one nugget is shown as indistinct cubic octahedra. The original "allopalladium " from the Harz Mts., supposed to be a hexagonal modification of palladium, could not be procured for a re-examination; it is probably the ordinary cubic palladium. A Simple and Accurate Constant-Volume Pyrometer for Specific gravity Determination. By DR. H. V. ELLSWorth. The pyrometer of 10 c.c. capacity is made of silica-glass, thus possessing several advantages over one made of ordinary glass. The stopper is perforated by a capillary and is continued into a graduated side-tube, which dips under water while the apparatus is cooling. The volume of the contained water to the graduations on the side-tube can be readily and accurately determined to 0.00002 c.c. The Optical Orientation of Labradorite from County Down (Ireland), Determined by the Fedorov Method. By W. CAMPBELL SMITH. The labradorite from basaltic dikes at St. John's Point, Ardglass, Co. Down, of which the chemical composition and refractive indices were published in 1912 has been studied by the Fedorov method and the optical orientation determined. Dr. C. E. Tilley demonstrated the inversion of CaSiO, in a metamorphic limestone from Larne, Co. Antrim (Ireland); and Mr. A. F. Hallimond exhibited an electromagnetic separator for mineral powders. GEOLOGICAL SOCIETY OF LONDON. The following communication was read at the meeting held on January 11, 1928 The Geology of South-Eastern Arabia. By GEORGE MARTIN LEES, M.C., D.F.C., F.G.S. South-Eastern Arabia consists of two separate tectonic and stratigraphic provinces (1) A foreland where, as at Dhofar, ancient gneiss is overlain by a Nubian type of desert-sandstone. The first marine transgression took place in the Cenomanian; (2) an orogenetic zone of typical Alpine character. The presence of nappes is indicated by great overthrusts, klippen, and by the stratigraphic differences between adjacent units. The movement is of pre-Gosau age. Upper Cretaceous and Tertiary strata lie with strong, often vertical, unconformity on the older Mesozoic and Palæozoic rocks. The stratigraphy of the orogenetic zone consists of: (i) A series of pre-Permian formations of unknown age. (ii) Permian dark-blue and black fossiliferous limestones. Near Jebel Rais limestones of a different facies appear as tectonic klippen; they are Crinoidal, Coral, Bryozoonal, and Neoschwagerina lime stones. (iii) Upper Triassic limestones, sandstones, and shales. The fauna consists of lamellibranchs and gasteropods; no ammonites have been found. (iv) Jurassic to Lower Cretaceous massive limestones. (v)? Upper Jurassic to Lower Cretaceous shales, sandstones, and red and green radiolarites. This group probably belongs to a different tectonic unit from (iv). (vi) Hatat Schists. A series of calc- and sericite-phyllites of unknown age, probably Mesozoic, which appear as a tectonic window at Saih Hatat. (vii) Basis igeneous series-lavas and intrusive rocks. (viii) Unconformable Upper Cretaceous to Miocene conglomerates, limestones, and marls. The Maestrichtian is exceptionally fossiliferous. The relation of Oman to the Zagros arc is discussed. The characteristic zone with red and green radiolarites and shales and basic igneous rocks occurs again in Persia, and forms great tracts of country south-west of Kerman. Here also Upper Cretaceous rocks are strongly unconformable. One great branch of the Cretaceous orogenetic zone of Central Persia must, therefore, have passed southwards into man. The Upper Cretaceous-Tertialy geosyncline broke down across the older strike, and pursued an independent direction parallel to the present Persian Gulf-Mekran coast. The late Pliocene movements also followed this trend, the influence of the older tectonics only being shown in the marked swing of the strike betwen Bandar Abbas and Jashk. Such a complete independence of these two phases of Alpine movement is unique. The Oman orogenetic zone may be followed through Masirah Island to Ras Madhraka, where it passes southwards into the Arabian sea. The Kuria Islands belong already to the foreland. A further movement, though of much less intensity, took place in Oman in post-Miocene time. South of Sur these folds strike north-west and south-east, and appear to pass out to sea at Ras al Hadd, independent of, and across, the older structures. Perhaps these folds form a continuous loop with the Kirthar Range of Sind, but no connection can have existed between the latter and the Cretaceous orogen of Oman. The Triassic, Lower, and Upper Cretaceous fossils are described. They include twelve new species. THE OPTICAL SOCIETY. At the meeting of the Optical Society, held at the Imperial College of Science and Technology, on Thursday, 19 January, 1928, the following papers were read :— On Toric Lenses. By T. SMITH, M.A., F.Inst.P., Optics Department, The National Physical Laboratory. A system of toric lenses having a common normal to all their surfaces possesses in general ten independent primordial coefficients. A single surface has only three degrees of freedom, and this number also holds for any system of negligible axial depth. Formulæ are given for the calculation of the ten coefficients, which are only all independent when the system includes at least three separated toric refracting surfaces with their planes of principal curvature finitely inclined to one another. An eye with both its cornea and its crystalline lens astigmatic and the meridians of principal curvature different has more independent coefficients than a spectacle lens has effective degrees of freedom. The nature and importance of the unavoidable residual errors in central vision when such an eye is corrected by a toric lens are discussed. Canonical Forms in the Theory of Asymmetrical Optical Systems. By T. SMITH M.A., F.Inst.P., Optics Department, The National Physical Laboratory. Canonical forms for the quadratic terms of the eikonal and of the characteristic function for any optical instrument are found to involve only six arbitrary con |