A NOVEL METHOD OF MEASURING THE COEFFICIENT OF THERMAL EXPANSION OF INVAR

Abstract

In a letter published in a recent issue of Nature, Prof. L. F. Bates and Mr J. C. Wilson, of University College, Nottingham, have described a new and novel method of determining the coefficient of thermal expansion of invar. Although this method is hardly likely to be applied to the measurement of the coefficient of expansion of long invar tapes, such as are used by surveyors, yet it is so novel and ingenious in itself that a short reference to it may not be out of place in this Review. One extremely interesting thing about it is that no measurements of a length, or of changes of length, are involved.     

THE DEFLECTION PRISM

Abstract

The optical principle of the deflection prism may not be known to all readers. Though there is nothing of very modern origin in the optics of a prism, as a wedge of very acute angle it possesses special powers which admit of useful adaptation to certain types of instrument. This application is a development of comparatively recent times. It will not be out of place, therefore, to make some reference to it in this Review.     

AN OLD FILE AND A NEW ARC

Abstract

In his article “Standards of Length in Question” published in the last number of this Review (Vol. i, pp. 277–-84) Captain G. T. McCawgave us most interesting and valuable history concerning the questionable past of the international metre. He has, it may be assumed, exhausted published evidence; but he states that he can find no reference to invitations from this country to France and Holland to send their fundamental standards for comparison with others at the Ordnance Survey in the eighteen sixties.     

EARLY MEASUREMENTS OF ARC IN ‘IRAQ

Abstract

In a tale, delightfully told in vol. ii, no. 8, pp. 121–2 of this Review, Mr. Kitching revealed how he was called upon to assist in determining the length of an Arab mile. In the notes following the story a reference was made to measurements of arc carried out in the ninth century A.D. The following notes add some more details to those already given. The full table of the Arab units of length is given below; in the reference above, one step was left out.     

THE CONFORMAL TRANSFORMATION OF A NETWORK OF TRIANGULATION

Abstract

In a recent issue of this Review, an example is given of the conformal transformation of a network of triangulation using Newton's interpolation formula with divided differences. While the application of the method appears to be new, attention should be drawn to the fact that Kruger employed Lagrange's interpolation formula in a discussion and extension of the Schols method in a paper which was published in the Zeitschrift für Vermessungswesen in 1896. A reference to this paper was given at the end of the paper, “Adjustment of the Secondary Triangulation of South Africa”, published in a previous issue of the E.S.R. (iv, 30, 480).     

GEODETIC SIGNALS IN SOUTHERN RHODESIA

Abstract

So much has been written in the Empire Survey Review and other publications on the somewhat controversial subject of “Luminous or Opaque Signals in Geodetic and Primary Triangulation” that it may be of interest to give an outline of the types of signals used on such work in Southern Rhodesia, with particular reference to the completion of the Eastern Geodetic Circuit in 1935 and the type of signal that it has been decided to adopt for future work.     

SOME EFFECTS OF PULLEY ECCENTRICITY IN BASE MEASURING APPARATUS

Abstract

The comprehensive paper on the suspension of tapes by M. Hotine in the January, 1939, issue of the Empire Survey Review (v, 31, 2) did not contain any reference to this question, as was pointed out by A. J. Morley in a letter published on page 261 in the same volume (v, 34, 261). A brief analysis has been made by F. Yates of the theoretical effects of pulley eccentricity and misalignment (“Gold Coast Survey Department Records” VoL III, 1931, page 43) but I have not seen any further reference to the subject and have recently experienced the effects of such a defect in our own apparatus, so the followingnotes nlay be of interest. Before proceeding to details I will describe briefly those parts of the apparatus which are considered here and give a short summary of the whole paper.     

SIR DAVID GILL AND THE GEODETIC SURVEY OF SOUTH AFRICA AND THE ARC OF THE 30TH MERIDIAN

Abstract

In the memoir of the late Capt. G. T. McCaw which appeared in the January number of this Review (vii, 47,2), reference was made to the part which the late Sir David Gill played in the origin of the work on the survey of the Arc of the 30th Meridian in Africa. This year is the centenary of Gill's birth, as he was born in June 1843, and it is therefore timely to give some account of his work during his long term of office as Her Majesty's Astronomer at the Cape which resulted inthe inception and completion of the Geodetic Survey of South Africa and the survey of the Arc to the southern shores of Lake Tanganyika. He died on 24th January 1914.     

A FIFTY-YEARS RETROSPECT

Abstract

The International Population Union.—In 1927, as President of the Geographical Association, it was my duty to deliver an address to the Association. I chose as my subject “Population and Migration” with special reference to the English-speaking peoples. One result of the publication of this in Geography, the journal of the Association, was that I was invited to attend the World Population Conference, which was held at Geneva in August-September 1927. The Conference was a very interesting affair. It was organized, and largely paid for, by Mrs. Margaret Sanger. About twenty-four countries were represented. The late Sir Bernard Mallet presided, and in one of his speeches, winding up the Conference, he truly said that we might “congratulate ourselves on having shown the world that population questions, which bristle with controversy, political, moral, and religious, can be discussed by sensible people without animosity or unseemly wrangling”.     

FIGURES OF REFERENCE FOR THE EARTH

Abstract

1. The object of this note is to clear up what I believe to be some misconceptions regarding the use of a reference system by a surveyor of the earth's surface. In his article “An Aspect of Attraction”, E.S.R., No. 7, pp. 24–8, Major M. Hotine expressed doubts as to the validity of the process usually followed. I may say at once that I consider these doubts are unfounded.     

THE EFFECT OF ALTITUDE ON TRAVERSE ERRORS

Abstract

I. These notes are the results of following up in some detail the well-known fact that the horizontal distance between two points at altitude h is greater, by an amount proportional to h, than the distance between the corresponding points at sea-level. Traverses based on rectangular coordinates are considered, with special reference to the residual errors left after adjusting the misclosures of such traverses without first eliminating errors due to altitude.     

TIDAL OBSERVATIONS IN CEYLON

Abstract

I. IN a Report which appeared in the Empire Survey Review, vol. i, no. 5, a short account was given on pp. 227-8 of the tidal observations which had been taken in Ceylon up to that time, with special reference to the selection of a datum for the geodetic levelling of the Island. The automatic tide-gauges at Colombo and Trincomalee were maintained in action till January 1934, giving five years of simultaneous continuous records of sea-level. The resul ts of an analysis of these observations may be of interest to readers. Where necessary, statements and figures appearing in the Report mentioned above will be repeated here, to make this account complete in itself and to avoid troublesome cross- reference.     

A Marriage is being arranged ...

Abstract

Experiments in computer-generated indexing techniques, with particular reference to The Cartographic Journal, are described.     

Terrain radiometric calibration of airborne UAVSAR for forested area

In the field of biomass estimation, terrain radiometric calibration of airborne polarimetric SAR data for forested areas is an urgent problem. Illuminated area correction of σ -naught could not completely remove terrain features. Inspired by Small and Shimada, this paper tested gamma-naught on one mountainous forested area using airborne Uninhabited Aerial Vehicle Synthetic Aperture Radar data and found it could remove most terrain features. However, a systematic increasing trend from far range to near range is found in airborne SAR cases. This paper made an attempt to use the relationship between distance to SAR sensor and γ-naught to calibrate γ -naught. Two quantitative evaluation methods are proposed. Experimental results demonstrate that variation of γ -naught can be constrained to a limited extent from near range to far range. Since this method is based on ground range images, it avoids complicated orthorectification.     

THE GEODIMETER: AN INSTRUMENT FOR THE ACCURATE MEASUREMENT OF DISTANCES BY HIGH-FREQUENCY LIGHT VARIATIONS

Abstract

The constant K in equation (12) represents distance expended through time lags in the instrument itself, and, although the value of K can be calculated from electrical data, this would not be very satisfactory and it would be better to determine it directly by means of observations over a line of known length. In addition, the point from which K would be reckoned is not a convenient one for actual field measurements. Instead of this, it is more convenient to choose an index mark on the instrument itself and referall measurements to this and thence to the mark over which the instrument is set up.     

TWO PROBLEMS OF RESECTION

Abstract

That admirable annual, The Surveyor (Ceylon), was generously forwarded to us some months ago. In this issue, vol. 2, no. 4, p. 93, there is given the solution of a question on resection in an examination paper. Since the solution appears rather laboured and the problem is interesting in itself and by no means valueless, it seems not out of place to attempt a simpler and more obvious answer.     

AN ASPECT OF ATTRACTION

Abstract

Measured deviations of the vertical have been used in support, or in destruction, of such pleasant little diversions as the theory of isostasy. They have also been used to adjust a triang~lation for swing, by methods which may fairly be criticized; but they have not, as far as I know, been used for reducing the horizontal measures of a triangulation to the standard conventional level of the spheroid of reference. In most cases such corrections would, of course, be too small to worry about, but it by no means follows that they are always small. In the case of a continental arc of meridian traversing a very disturbed mountainous region exhibiting certain constant tendencies, it should at least be demonstrated that they are small before the question can be considered finally settled.     

NUMBER ONE HUNDRED

Abstract

Readers will notice that this issue of the Review is numbered 100 and, as it has always been published quarterly, this means that it has now been in existence for 25 years and so celebrates its silver jubilee.     

ANTIPODES

Abstract

The following paragraphs may serve to show that there is more in the word antipodes than meets the eye. And it will be reasonable in an investigation of this sort to begin with some dictionary definitions. For this purpose let us take the definitions given in the “Oxford Dictionary”.