ALBERT

Notes: The paper discusses the variations of Elevation Correction Factors (E.C.F.) across various stratigraphical and structural occurrences with particular reference to the dipping bed, fault and horst. Graphs are prepared giving E.C.F. variations for various angles of dip and a method is suggested for application in the field. Errors in the linear variation that is commonly used for small angles of dip are discussed.The second part of the paper consists of the application to interpretation of (I) Change of gravity dip and (2) The gravity inversion. It is shown how from a gravity map the dip, position of outcrop and thickness of a dipping bed can be determined. The last part shows how anticlines can give rise to negative anomalies and that in the direction of dip similar structures can at one point have no surface expression and afterwards invert to positive anomalies. The danger of attempting to predict the size of structures in such areas is emphasised.

Notes: When gravimetric prospecting is concerned with a region featuring broken relief the calculation of topographical corrections becomes vitally important, for these rectify apparent anomalies completely. It is essential that they should be calculated as exactly as possible. By the classic method this takes an extremely long time and may in the long run involve an outlay actually higher than that expended on operations on the terrain.It has thus been felt necessary to seek methods which would speed up calculation, and, bearing that in mind, the use of a polar integrator has been envisaged. With this the contour lines of a map can be followed between two fixed radii, the pole corresponding to the location of the position. Two integrator roulettes will give the values of the first two terms of the expansion in terms of the quotient of the height divided by the distance, the second of the terms resulting from the curvature of the earth. Unless there are escarpments very close to the position, the use of these two terms will be sufficient.Polar integration will deal successively with different contour lines and a subsidiary graph will be plotted, giving the value of each of the integrals in terms of the height. By means of this subsidiary graph the values of the corrections will be obtained with a planimeter and a moment integrator. It is envisaged that the same operation could be repeated in the case of two maps with different scales, for instance, 1–20,000 and 1–200,000 the effect of the areas in the immediate neighbourhood of the position being taken into account by the observer. It is hoped that in this way the calculation of topographical corrections will be made quicker, more exact and less laborious.

Notes: The problems connected with reflexion surveys in areas of rough topography consist of choosing proper equipment and of making careful near-surface corrections. This paper illustrates some solutions to these problems that have been adopted in a survey which has recently started in a hily coastal area, in Southern Italy.As the area is characterized by a youthful and very actively eroded topography of Post-Miocene clays and litoral clastic sediments, both rotary and percussion drilling were necessary whilst all the seismic equipment had to be light to allow straight lines to be shot as far as possible. Details are given of the truckmounted, light equipment which has been designed for this special purpose.In connection with the youthful topography of the area being surveyed, the criteria for the proper computation of the near-surface corrections is discussed. The great differences in elevation, combined with variations in the surface and near-surface materials, necessitated a careful analysis before deciding the thickness of the correction zone. The results are shown of the preliminary tests carried out in order to determine the average thickness of the low-velocity zone. The solution adopted for drawing the reference surface determining the base of the correction zone for the whole of the area is subseqently explained.Reference datum is drawn so as to follow gently, and with segments of constant slopes, the general features of the rough topographic relief at a depth ranging from 30 to 60 metres from the surface. Criteria for the routine checking of velocity variations in the correction zone are illustrated. Such checks are based on both uphole time analyses and refraction “first breaks” plots, with deeper shot holes at constant intervals.Unsatisfactory results necessitate longer spreads for “low velocity tests” and uphole shooting from deeper holes and the reference datum is deepened for the particular area where this becomes necessary.The final cross-sections are shown and although, as yet, no deep holes, are available to check the seismic data, the general appearance of the cross-sections seems to indicate that subsurface data are free from the influence of topography and of the velocities in the near-surface formations.

Notes: The paper describes the determination of the chlorine content of deep ground water by means of the direct resistivity method using the Wenner electrode configuration. The purpose was to investigate the distribution of salinity in the brackish waters within a permeable sand of thickness 250 metres and which forms the deeper subsoil of the Ysselmeer areas.Such a knowledge is of great value, firstly because the seepage of salt water into the proposed deep “polders” may reduce the crop yield, and secondly because it allows areas, where potable waters may occur, to be delineated.To test the method, measurements were made near existing boreholes which extended to a depth of 350 metres. From these borings water samples from various depths were collected and it was found that the resistivity pl of the porewater was closely related to their chlorine content. The resistivity p of the saturated sand was determined from the geo-electrical measurements. It was found that the resistivity p was given by p= 4, 5 pl. From this relation, which is independent of the salinity, the chlorine content of the porewater could be estimated. These results are in close agreement with those of other observers. In the area p varied from 1 to 200 ohmmetres corresponding to a chlorine content changing from 12.000 to 15 mg per litre.The method was adapted for working over water. Each of fourteen insulated conductors in a special cable terminated in an electrode, and these electrodes were spaced along the cable so that nine different Wenner spacings could be selected. The electrode separations varied from 44 metres up to 306 metres.

Notes: The authors develop an optimum filtering theory for seismic reflection recording. A criterion of record improvement is applied to a mathematical model consisting of a set of wavelets superimposed on a random noise backgruond. This leads to the design of electrical filters and geophone and shot-hole patterns with optimum filtering characteristics.

Notes: The paper describes and discusses the results of an experimental gravity survey which was carried out underground on different levels of a mine, in the mine shafts, and on the surface above the mine workings.The paper is composed of three complementing sections. The part dealing with gravity measurements in the shafts gives also attention to the particular problem of the terrain corrections underground, due to the surface topography. The interval densities from gravity measurements in the shafts are computed and adjusted in accordance with known geology and compared with the stratigraphical columns of the shafts. The effect of the ore body on the stations in the shaft is derived theoretically and compared with the observed one.The gravity contours are constructed on different levels in the mine workings and discussed in relation to the known extent of the ore body. The gravity profile across a fault underground is presented and discussed. Another gravity profile was run underground in the same plan position as a surface traverse 1000 feet above it. The line of boreholes along this traverse gives good account of geology which includes step-faulting. This known geology is compared with the deductions based on the gravity results. This is also done in the case of another gravity profile run over a known geological section. A number of gravity measurements were also taken in the same plan position, separated by the vertical distance of 800–1,100 feet. These points were placed by the boreholes previously drilled in the area. Attempt in correlation of these and gravity results is made.The densities computed from the gravity measurements are compared with the laboratory determinations of the densities, carried out on samples from different parts of the mine.The contours on the top of the base formation are constructed from the information obtained from the boreholes, and are compared with the gravity contours on the surface above.A simple method of computation of the effects of slabs and blocks is presented as applied to the calculation of the corrections for underground drifts and faults. A table is appended for use with this method.

Notes: The gravity difference between two stations, one at the surface and the other underground vertically below the former and at a given distance from it, depends on the mean density of the earth, σm as well as on the density of the layer of rock contained between the two stations. When one of these densities is known, the other can be computed from this gravity difference. The reliability of this determination depends on the relative accuracies with which σm and σ can be obtained.These accuracies are discussed in the paper. The mean density of. the earth has been determined with an accuracy of approximately 0.01 gr/cm3. The determination of the density of a layer of rock depends on density determinations of rock samples which are not representative of the layer as a whole. Thus the accuracy of the value of σ based on a number of sample determinations will depend on many factors, including the method of averaging the density values obtained from the samples and the degree of uniformity in the geology.To investigate the problem discussed above, three sets of gravity measurements were made under differing conditions. In each instance a number of pairs of stations vertically above each other were occupied on the surface and underground. The results computed from the data on each pair of stations in a set of measurements were considered as repeated measurements of the same quantity, and the most probable value was calculated.The results demonstrated that the accuracy varied with the conditions prevailing in the area where the observations were made. In Godstone Quarries the dip of the strata was negligible, the rocks fairly uniform and structural conditions undisturbed. Consequently, although the rock layer between the surface and underground stations was only of the order of a hundred feet, the mean density of the earth computed from the average density of the rock samples, was very close to the accepted standard value of 5.52 gr./cm3. This agreement, however, was easily upset when only one random sample density was assumed as representative of a given formation.In a different locality in Cumberland the observations were made in a mine and on the surface. The rock layer between the surface and the underground stations was approximately a thousand feet thick. One set of measurements followed a line parallel to a fault, the other a line crossing this fault. The results differed appreciably from the standard value of σm, particularly in the latter case.It is concluded that the gravity difference between a surface and an underground station can be used satisfactorily to determine the average density of a rock layer in situ and en bloc, using the standard value for the mean Earth density.

Notes: In this paper we describe a protractor which provides a very simple method of constructing refracted rays in a vertical plane. Another advantage of this apparatus is that it can be made locally in any computing office.

Notes: A method is described for computing master resistivity curves. It is a modification of that devised by Ehrenburg and Watson, but is superior as a shorter time is required for the computations. A collection of 31 master curves for the three layer case is presented.

Notes: On the basis of results of extensive geoelectrical investigations in East Frisia as well as of theoretically calculated data, it is shown to what extent geoelectrics can furnish a contribution to success during the preliminary work for the establishment of water works, or for the enlargement of existing water works, in coastal areas. One of the most important tasks in this sphere is the search for permeable beds suitable for intake, the delimitation of their thickness and extent (catchment areas), and then the location of favourable places for wells. This task is rather difficult because of thickness variations in and change of facies of the old-pleistocene basin clay (Lauenburg clay) and the presence of Tertiary clay and fine clayey sands which, acting as impervious layers, often divide a permeable bed into several storage horizons. Further difficulties arise from the occurrence of brine bearing deposits near the coast, and water from the depths with a high salt content as a result of leaching processes around salt domes.The problems arising in this connection are illustrated with the aid of examples from the Rheiderland. The following questions seem to be the most important:a) the physical interpretation of the measurements with special regard to the principle of equivalence;b) the correlation of the physical data with the subsurface geology.

Notes: This paper describes a highly portable geophone, designed for large-scale refraction surveying, which uses a novel suspension system to obtain a natural frequency of about 1.85 c/s. The nominal output is 0.7 volts/cm/second into a 500 ohm load, the damping then being 0.7 of critical. Some typical recorded arrivals obtained with this geophone are illustrated.

Notes: To improve the ratio of signal to noise resulting from the shot, seismologists have increased the number of geophones in each recording channel and have also increased the length of each spread. As a rule, however, the effectiveness of this multiple recording is based on theoretical considerations, and it appeared desirable to carry out an experimental investigation to obtain a direct measurement of the reduction in noise as a function of the geophone pattern etc. The work was done in the Landes where experience had shown that recording was difficult.The experimental arrangement, which allowed the accurate measurement of the noise without interference from reflected energy, is described.Shots, repeated under apparently identical conditions, revealed the random nature of the noise and pointed to the necessity of a large number of experiments to yield an accurate result. Two geophone patterns were employed, one of 12 geophones in a straight line and the other of two parallel lines of geophones, the directions of the geophone lines being either along the shot line, perpendicular to the shot line or at some intermediate angle.The results obtained, in two widely spaced locations were in good agreement and allowed definite conclusions to be drawn. When the 12 geophone line is long enough the noise is reduced by a factor of 0.36 and with two lines, each 55 metres long and containing 12 geophones, the reduction was 0.29, if the lines were sufficiently widely separated. The results agree with the factor K N-½ for the reduction in noise where N is the number of geophones per trace and K is a factor close to unity. The results also show the influence of the length of the geophone line its orientation and its mean distance from the shot.

Notes: For the first time a method of observing the effects of hammering and of small blasts has been applied in a series of experiments on various soils, using a three component set of small mechanical leaf spring seismographs. The seismograms have been subjected to a thorough harmonic analysis. By means of these experiments, the theoretical concept of Rayleigh waves generated in a layer overlying a semi infinite medium has been confirmed. The dispersion curves resulting from different experiments correspond well with theoretical dispersion curves.It may be. concluded that every seismic pulse generates a specific Rayleigh wave mechanism in loose layers. The depth of penetration of the Rayleigh wave mechanism and its frequency spectrum depend upon the delivery of energy and upon the consistence of the particular soil.Most of the energy delivered is transformed into surface-waves, and it is obvious that the direct reading of pulses in seismograms effects mainly group velocities of the Rayleigh wave mechanism. Thus, all endeavours to procure information about near surface layers of loose soils by refraction seismic work, as the present investigations show, meet with far more difficulties than has been assumed in the past.With regard to the determination of the critical frequencies of the generated surface waves, the method of harmonic analysis of seismograms is superior to the usual dynamic method of soil mechanics, since rotating weights do not give the characteristic phase velocities and transversal wave velocities necessary for judging the consistency of loose soils.Finally, a method of determining the absorption of surface waves is discussed.

Notes: Book review in this articleA. S. Eve and D. A. Keys. – Applied geophysics in the search for minerals. Cambridge University Press. Fourth edition 1954.

Notes: Book review in this articleL. W. Sorokin. – Lehrbuch der Geophysikalischen Methoden zur Erkundung von Erdölvorkommen.M. R. J. Wyllie. – The fundamentals of electric log interpretation. Academic Press Inc. – New York, Sept. 1954. Price $ 3.60.

Notes: The problem is considered of how to determine, from dip shooting data, the position in space of a reflecting horizon located underneath a refracting interface between two media of different velocities.The author proposes a combination between a geometric solution and an analytic one, to obtain the quickest result.

Notes: Calculations are presented of reflection coefficients of plane longitudinal waves incident at oblique angles on boundary planes between elastic media. It is shown that the manner in which these reflection coefficients vary with the angle of incidence is strongly affected by the values of the Poisson's ratios of the two media. It appears that, contrary to a conclusion arrived at by Muskat and Meres, the reflection coefficient may vary appreciably with the angle of incidence in the range between O° and 30°. Possibilities of practical application of this phenomenon are discussed.

Notes: The group velocities of Rayleigh waves, as measured by Rohrbach on the Göttingen records of two Asian earthquakes for which the azimuth of arrival was from the East, have been discussed in terms of a two-layer model, in which the upper layer, of granite of thickness T1, rests on a basaltic layer of thickness T2, with ultrabasic material below extending to a great depth. The wave velocity equation, in the form of a ten-row determinant, was solved by means of the EDSAC electronic computing machine of the Mathematical Laboratory, Cambridge; the ratio c/β2 of wave velocity to distortional wave velocity in the T2 layer was calculated for a sequence of values of KT1, for the three values I, 1/2, 1/3 of the ratio T2/T1. The values for T2, = o on slightly different data were available from earlier work. The group velocity was obtained from the wave velocity by numerical differentiation.For the earthquake of 1930 July 2 in Eastern Bengal the mean values of T1 over the whole range of periods from 65.3 sec to the shortest periods that the dispersion curves permitted (24 to 27 sec) were respectively 27.1, 30.6, 32.7 km on the three hypotheses, with 37.8 km for T2= o. The internal consistency of the results is in favour of the third case, with T1= 32.7 km; T2=10.9 km. The independent evidence of other lines of investigation favours a continental structure with a granitic layer 30 to 35 km thick and a basaltic layer of small or zero thickness; studies of near earthquakes and of large explosions suggest that the intermediate layer may be of only local occurrence. These determinations fit closely an empirical formula T1+0.35T2=36.3 km.The corresponding thicknesses derived from the shock of 1924 July 11, in the Kuen Lun Mountains, are a little smaller and are closely represented by the formula T1+0.646T2=36.6 km. Since the waves from Eastern Bengal traverse the Himalaya region this difference is to be expected.The results fully justify the use of seismograms that record the vertical component of motion, and indicate the desirability of further research along these lines.

Notes: The free (420d) nutation is known to be heavily damped, the characteristic damping time being less than ten periods. The origin of this damping is unknown, but must be due to dissipative, non-rigid-body movements of the Earth. The view, which has been widely held, that this may arise from the relative motion between the liquid core of the Earth and the mantle is shown to be based on an error. When account is taken of its small moment of inertia, the core cannot be held responsible for this damping, nor can a limit be derived for its viscosity. This confines the origin of the damping to a non-elastic behaviour of the mantle.

Notes: In the development of seismic drilling methods in Northern Italy the most important considerations have been those of ease in transport and quickness of operation. Different drilling systems are described that are adapted to the different types of near surface formation that are encountered in the area. In soft sands a high pressure water jet is used, a rotary table not being required in a great many cases. In medium consistency sand and small gravel, the drill rods are rotated by a special roller wrench equipment instead of the more usual kelly. In coarse formations, gravel and boulders, casing is driven by special pile driving equipment with collapsible mast for easy transport.

Notes: Velocity functions can be grouped into families, any One of which results, in seismic pictures differing among themselves only in their scales of time and distance but similar in all other respects. For any one of these families it follows that curves drawn on logarithmic scales of time and distance to represent a particular relationship between seismic quantities will be similar in shape. This leads to the use of templates with logarithmic scales for fitting a smooth velocity function to a set of seismic data. Suitable templates for fitting refraction and reflection data to velocity distributions linear with either depth or vertical time are presented. An insight into the uncertainties involved is obtained with the aid of numerical examples.

Notes: This paper deals with the four electrode method of electrical resistivity prospecting using direct current. It is shown that three resistances can be measured for any four electrode configuration, and a simple relation between them is derived. The particular case of the Wenner electrode configuration is discussed and a further relation derived between the three apparent resistivities corresponding to the three resistances. The practical value of the -resistance relation as a means of avoiding experimental errors is indicated.In general the three apparent resistivities are different in magnitude although there are certain particular cases where they are equal to one another. Their actual values are determined for a number of simple problems and the possibility of having a negative apparent resistivity is illustrated.Finally, examples of field tests are given in which the three resistances were measured, and it is concluded that the method can often provide a simple way of distinguishing between the effects of lateral and vertical resistivity variations.

Notes: An analytical treatment is given of the response of linear arrays of multiple geophones, as a function of the direction of incidence of the wave and of the wave frequency. The relation between the response and the direction of incidence may be quite complicated, the response being zero in several directions. As a function of wave frequency, the response may also have several zero values within the frequency band in which reflections are expectable. This would result in a serious modification of the filter characteristics of the amplifier. It is shown, however, how such a modification of the filter characteristics may be avoided by a judicious choice of the number and the spacing of the geophones in a multiple group.

Notes: It has been noted that in water-saturated silt, the velocity of propagation of longitudinal waves is very low. The purpose of this paper is to suggest a theoretical explanation for this phenomenon.The medium under study is assumed to consist of identical solid spheres piled one upon the other in a regular array, with the fluid filling the interstices. First the velocity of propagation is calculated for the system of the solid particles alone; then, utilizing the results obtained for this case, the velocities for the solid-fluid system are calculated. Two velocities are obtained, one of them being higher and the other lower than in the case where no fluid is present.

Notes: Book review in this articleH. Faul Nuclear Geology. A Symposium on Nuclear Phenomena in the Earth Sciences, John Wiley and Sons, Inc., New York, 1954 Price $ 7.00.

Notes: Hazards due to powerlines, radiotransmitters and self-potentials in connection with weather conditions are considered. Voltage and current values are given for several measurements made under the most severe conditions of circuit arrangements. The necessity of general safety precautions is stressed.

Notes: For the quantitative interpretation of field resistivity curves it is necessary to possess theoretically calculated standard graphs. The problem of calculating such graphs for certain parallel stratified media has been solved long ago. The methods developed so far, however, require facilities, which are not normally available to the geophysicist in the field. It has been shown by experience, that the catalogues of graphs, which have been made available for practical use, are inadequate, when the number of layers exceeds three. For this reason endeavours are made to find a method, to allow the geophysicist to calculate model graphs suited to any given special geological situation, with ordinary field facilities and without too great an expenditure of time. The principle of equivalence implies that such a model graph be known with a high accuracy.To this end, a method for the calculation of model graphs for a series of parallel beds is described. This method is sufficiently simple – no series need to be summed up – to be applied by the geophysicist in practice, even during field work. The study of the kernel function in Stefanescu's integral representation of the “apparent” resistivity leads to a basis for the set of graphs. The prime elements of this basis form a one-parametric curve-system, by means of which the graph for any multi-layer sequence of strata can be obtained to any degree of approximation by linear combination.The importance of this method in practice is demonstrated with the help of examples.

Notes: The paper describes a geometrical construction which allows the reflecting or refracting Tsoundaries to be derived from seismic time observations.In reflection work the construction makes use of the ray reflected from the boundary at normal incidence. For constant velocities of the beds, or for a linear increase of velocity with depth, the method leads to the construction of successive envelopes from which the reflecting interface and the rays are obtained. By using the idea of “stretching fictitious rays”, the construction requires ruler and compasses only and is applicable to both plane and curved boundaries with any strike direction and in any number.The same principles can be applied to refraction problems and again the. construction of successive envelopes allows the indirect or Mintrop wave to be defined. The position of the refracting boundary and the velocity can be derived immediately. As in the reflection method any number of plane boundaries with any strike can be dealt with.An appendix discusses the use of the method in reflection work with any type of velocity distribution.

Notes: The directions of remanent magnetization of samples taken from a number of varved clay series from Sweden have been measured in an attempt to obtain information about the direction of the Earth's field in past times. Two sets of samples were taken with a Kullenberg core sampler from cores of recent varves obtained from a river delta. It was possible therefore to compare the magnetization directions of these samples with observatory records of the Earth's field direction at the time of deposition of the clay. The results indicate that the magnetizations were acquired on deposition and have remained stable in direction since. Their directions are shown to have been controlled not only by the Earth's field but by the slope of the bed on which deposition took place and very probably by bottom currents flowing in the river or lake during sedimentation. Thus no information about the past direction of the Earth's field can be obtained from the data unless corrections can be applied to allow for these factors. A method of correcting approximately for the change of magnetization direction due to deposition on a slope is explained. No way of allowing for the effects of bottom currents has yet been discovered, though there is evidence that in some instances these effects are small. Where this is so the magnetization direction may perhaps prove a reliable indicator of the field direction at the time of deposition.

Notes: Refraction diagrams for 6-s microseisms are drawn for the island of Bermuda. It is assumed that the waves are surface waves between the ocean and the sea bed of the type first described by Stoneley, so that the shallower the water the greater the wave velocity. The diagrams show that the effect of refraction on the energy of the incident waves is very marked, particularly for waves approaching from the N-E and S-W quadrants. This effect explains some of the anomalies that have been found at Bermuda.

Notes: Experiments are described in which samples of unconsolidated glacial deposits from Sweden were redispersed and allowed to settle in a tank. The direction and intensity of the resultant magnetic field were varied and currents were created in the tank in an attempt to discover what factors, other than the magnetic field, control the alignment of the permanently magnetized particles which give the sediment its remanent magnetic moment.Two such factors were found to be important, namely the slope of the surface on which the sediment was deposited and the velocity of the current immediately above this surface. A tentative theory of the effect of slope is put forward which accounts almost quantitatively for the experimental results and in addition leads to a qualitative explanation of the effect of bottom currents.The relationship of these results to measurements of the direction of the natural remanence of the same material is discussed.

Notes: The I.S.S. for 1935 records a series of seven earthquakes with the same epicentre off the east coast of Japan. This series, in which the I.S.S. identifies many arrivals as P* or S*, was examined in the hope of estimating velocities of P* and S*. Straight lines fitted to first arrivals at stations of azimuth 180° to 270° gave the local velocity of P as 7.77 ± 0.04 km/sec. Epicentre and origin-time were then redetermined for each shock, and revised times of arrival plotted against revised epicentral distances. The following conclusions were reached:〈list xml:id="l1" style="custom"〉No series of arrivals could be identified as P* or S*.The redetermined epicentres show an approximately linear arrangement. The uncertainty in position of each epicentre is comparable with the distance between successive epicentres, and may be due to the spatial extent of the focus.There is a clustering of points between Δ=4° and Δ=9° about a line which would represent a pulse travelling with the velocity of S but 15.8 sec later than S. The delay may be used to obtain an estimate of the depth of the Mohorovičié discontinuity.

Notes: Previous theoretical work on features of seismic rays has been extended to the case of pP and PP rays. It is shown that, for a wide class of velocity variations in the Earth's outer mantle, there is a cusp in the pP travel-time curve which corresponds to a ray which leaves a focus at finite depth in a direction inclined at a finite angle above the horizontal through the focus. It is also shown that the cusp is in general theoretically similar to the cusp in the PKP case. A method is given for locating this cusp for particular focal depths and is illustrated in an application to the Jeffreys-Bullen travel-time data. The general influence of the 20° discontinuity is discussed. Comment is made on conventions in naming pP and PP rays.

Notes: Using the Worden gravimeter belonging to the Geological Survey, the differences of gravity have been determined between the Ordnance Survey Office, Southampton, and St Anne, St Peter Port and St Helier, in the Channel Islands. The values of gravity at the three new stations, referred to the Potsdam system, are found to be:- 〈displayedItem type="mathematics" xml:id="mu1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:0956540X:GJI76:GJI_76_mu1"/〉

Notes: A re-examination of the gravity values relative to Cambridge at the primary stations York, Newcastle-upon-Tyne, Edinburgh and Aberdeen has shown that the errors of the pendulum observations (Browne et al. 1950) at these places, with the exception of Newcastle, are well within the published standard deviations, while the error at Newcastle only just exceeds twice the published standard deviation. The calibration factor of the gravity meter used in the investigation has been found by comparison with the pendulum values to be consistent with the tilt-table value determined by the maker. The new measurements suggest that the uncertainties given by Cook (1953) in his adjustment are realistic. By combining the present observations with the pendulum values and the differences measured by Bullerwell (1952) new gravity values have been calculated for the four stations.

Notes: Methods of using isotopic abundances of dated common lead samples to obtain the time since which the Earth's upper mantle has preserved heterogeneities in its composition are reviewed. This time has often been referred to as the “age of the Earth”. Several modifications of these methods are suggested. The measured abundances of eighty young lead ores are examined in detail, and it is concluded that the age of the Earth is 4.3 × 109 years.