NOTES ON LEVELLING WITH THE ANEROID BAROMETER

Abstract

In chapter 5, page 12, of my “Report on a Rapid Geological Survey of the Gambia” (Gold Coast Geological Survey Bulletin, NO. 3) I have stated the opinion of Prof. Julius Hann of Vienna that the barometric curves may be analysed into two components:- <list list-type="alpha"> <list-item>

semi-diurnal, constant, depending on latitude and altitude (with a slight yearly alteration);</list-item> <list-item>

diurnal, depending chiefly on temperature (and humidity ?).</list-item> </list>     

FURTHER NOTES ON FIGURES OF REFERENCE

Abstract

Major Hotine (E.S.R., No. II, pp. 264–8) still finds the location of a reference spheroid to offer insuperable difficulties. I confess that my difficulty is to see his! In my previous article (E.S.R., No. 8) at the foot of page 76, I used the word “coincidence” in error for “parallelism”. This harmonizes the article and I am glad that Major Hotine has directed attention to the error.     

A FIFTY-YEARS RETROSPECT

Abstract

The Ordnance Survey and the War.—I shall not inflict upon the readers of this Review any very long account of the work of the Ordnance Survey during the Great War. At that time the work of the Survey suffered from one necessary disadvantage: all the young men on its establishment, whether in the R.E. Companies or on the Civil Staff, left for active service. As a slight compensation for this inevitable dislocation all money difficulties in the preparation of maps for war disappeared.     

STONEHENGE AND WOODHENGE

Abstract

Owing to the kindness of the editor, I have recently been able to see the article on Stonehenge and Woodhenge by Captain Learmont, together with the editor's notes in the Empire Survey Review for April 1936. I hope the editor will also allow me space to make a few comments.     

THE CONVERGENCE OF MERIDIANS

Abstract

Some publications that have dealt with the question of convergence of meridians seem, to the present writer, to be clouded with misconception, and these notes are intended to clarify some points of apparent obscurity. For instance, A. E. Young, in “Some Investigations in the Theory of Map Projections”, I920, devoted a short chapter to the subject, and appeared surprised to find that the convergence on the Transverse Mercator projection differs from the spheroidal convergence; the explanation which he advanced can be shown to be faulty. Captain G. T. McCaw, in E.S.R., v, 35, 285, derived an expression for the Transverse Mercator convergence which is equal to the spheroidal convergence, and described this as “a result which might be expected in an orthomorphic system”. Perhaps McCaw did not intend his remark to be so interpreted, but it seems to imply that the convergence on any orthomorphic projection should be equal to the spheroidal convergence, and it is easily demonstrated that this is not so. Also, in the second edition of “Survey Computations” there is given a formula for the convergence on the Cassini projection which is identical, as far as it goes, with that given for the Transverse Mercator, while the Cassini convergence as given by Young is actually the spheroidal convergence. Obviously, there is some confusion somewhere, and it is small wonder that Young prefaced his remarks with the admission that the subject had always presented some difficulty to him.     

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 FIFTY-YEARS RETROSPECT

Abstract

The Ordnance Survey after the War.—I might class the four years after the War, during which I remained at the head of the Ordnance Survey, as interesting but troublesome. As is well known, an entirely unreasonable impression was spread about that, now that the War was over, there would be a period of great prosperity, and that we should all live like fighting cocks. Well, things did not work out like that. There was a Select Committee on National Expenditure (1918), and this Committee recommended a lengthening of the period of revision of the large-scale maps of the United Kingdom and a consequent, ultimate, reduction of establishment by 500 men. The Treasury later on insisted on a reduction by 600, including Ireland.     

LATERAL DISPLACEMENT OF SIGNALS OBSERVED

Abstract

I notice that in the last two numbers of the Empire Survey Review a lateral displacement is mentioned or implied.     

THE POST-WAR PROGRAMME OF THE ORDNANCE SURVEY OF GREAT BRITAIN

Abstract

In 1938 the committee to investigate the activities of the Ordnance Survey, presided over by Lord Davidson, issued its final report. One of the terms of reference of this committee was “to review the scales and styles of Ordnance Survey maps placed on sale to the public and to recommend whether any changes are desirable”.     

THE ENGINEER SURVEYOR

Abstract

Survey Training for the Civil Engineer at the University has been discussed in four articles in the Review. (R. N. Ray, M.A., xii, 89, 104–110; H. Biesheuvel, B.Sc., xii, 90, 159–165; A. Stephenson, O.B.E., M.A., F.R.I.C.S., xii, 91, 217–222; K. R. Peattie, B.Sc., Ph.D., A.R.T.C., A.M.I.C.E., xii, 94, 376–379.) Cost of equipment for a large class and limitation of time in an already heavily loaded curriculum prevent the student acquiring enough training to undertake the survey work required on alarge engineering scheme. The schemes of training described in the four articles are greatly to be admired and it is hard to see how any improvement can be made.     

UNITS OF LENGTH AND AREA,III

Abstract

In two papers on this subject (v, 34, 236, and vi, 40, 85) some difficulties were examined and missing evidence explored. Reference was made to the past existence of divers acres in the British Isles. In a lecture by Professor A. E. Snape, M.SC., on “Our Units of Measurement”, delivered at the University of Cape Town and printed in the South African Survey Journal (III, Part viii, 24, 340, 1930), some other units are considered and additional evidence adduced. For example, the Cheshire acre is given as 2.11 statute acres.     

THE TRAINING OF AFRICAN SURVEYORS IN NIGERIA

Abstract

Whenever the Government wants to receive new students to be trained as surveyors for the Government Service it is usual for the public to be informed by means of a Gazette Notice outlining the conditions of entry into the Survey School which is attached to the Land and Survey Department. Nowadays students are admitted through the Government Higher College at Yaba by means of the Entrance Examination of that college. It is one of the conditions that before a candidate applies to take this Entrance Examination he must have passed his Cambridge School Certificate Examination, the Matriculation Examination of any British University, or its local equivalent, and must possess also a certificate of character.     

INTERPOLATING FROM TRAVERSE TABLES TO SECONDS

Abstract

In the Empire Survey Review, no. 4, 1932, Mr. Clendinning has described a method of interpolating from traverse tables to seconds. Below is another method, due to Prof. Nekrassov, for use with traverse tables published by him. The method is described in The Geodezist, Moscow, 1936, no. I, pp. 47–52.     

TRIALS OF A SURVEYOR-MODERN VERSION

Abstract

Reading the Empire Survey Review of 20 years ago, with the tales of raw jungle and untrodden country, as in Sir Charles Arden-Close's retrospective accounts, I am tempted to give a brief picture of surveying in the Colonies today, away from the beaten track.     

CURVATURE AND REFRACTION TABLES FOR TOPOGRAPHICAL SURVEYS

Abstract

In a series of articles published at different times in the Empire Survey, Review, the writer has stressed the utility of the slide rule in topographical work for both mapping and engineering purposes. It is his opinion that every topographical surveyor should be thoroughly conversant with the slide rule, and that there is no difficulty in teaching anyone, even with limited educational qualifications, all that is necessary about if. One advantage of its use is that the plotting-scale divisions need not represent any simple multiple or fraction of the normal units of length, but can be chosen so that the subdivisions cause no undue eye strain. This plotting scale can then be used for work on any scale, all necessary tables being calculated and constants adopted for use with it, without any extra work being required. A scale of I/250 (I foot divided into 25 main and 250 minor divisions) was found to meet the case.     

THE SCHOOL OF MILITARY SURVEY AND ITS COURSES FOR COMMONWEALTH SURVEYORS

Abstract

On the first of January 1949 the Survey Training Centre of the Royal Engineers became the School of Military Survey. In the previous two years over fifty Colonial Survey Officers or Probationers came to the Training Centre as students on various courses. Many of these have now taken their places in the Colonial Survey Service. More students may come in the future not only from the Colonies but also from the Dominions, for just as the Military Survey courses are open to the military officers of the Dominions so are the Colonial Survey courses open to the survey students from the Dominion Governments. Some information about the School and courses may be of interest to these potential students and to many readers of this Review, and these notes have been written with the intention of providing this information     

PRACTICAL APPLICATION OF THE LAPLACE LONGITUDE-AZIMUTH RELATION TO CONTROL OF GEODETIC ANOMALIES

Abstract

1. In geodetic work a ‘Laplace Point’ connotes a place where both longitude and azimuth have been observed astronomically. Geodetic surveys emanate from an “origin” O, whose coordinates are derived from astronomical observations: and positions of any other points embraced by the survey can be calculated on the basis of an assumed figure of reference which in practice is a spheroid formed by the revolution of an ellipse about its minor axis. The coordinates (latitude = ?, longitude = λ and azimuth = A) so computed are designated “geodetic”.     

A TEST FOR THE RELIABILITY OF TRIGONOMETRICAL OBSERVATIONS

Abstract

I should like to reply to the Editor's comments on the above article, published in the E.S.R., v, 34, 226 (October 1939).     

THE TOWN PLANS

Abstract

The town plans in question are those ranging from the “five-foot” (1/1056) to the modified “ten-foot” (1/500) scales, made by the Ordnance Survey between 1841 and 1894, and then, in principle at any rate, abandoned. This is, I fear, wholly a British matter and profuse apologies are offered to oversea readers. Yet history, repeating itself as usual, may presently add the wider interest to the tale.     

TRIGONOMETRIC HEIGHTS AND REFRACTION

Abstract

In the past there has been considerable discussion on the above subject in this Review. There is a bibliography at the end of this article in which the full titles of previous articles are given. For brevity, reference to them in the following text is made by number only. Recently, Gulatee summarized present knowledge and asked how other Survey Departments dealt with this matter. Consequently, it was considered that it would be helpful to set out in detail the procedure adopted by the Directorate of Colonial Surveys for obtaining trigonometric heights, with particular reference to primary and seoondary chains and nets.