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.     

THE LEVELLING OF A THEODOLITE

Abstract

A Fully equipped theodolite is provided with plate levels, an alidade level, and a striding level. An instrument not so equipped has no title to be considered a “Universal Instrument”, that is to say, an instrument designed for every kind of both terrestrial and celestial measurement. Without a striding level, for example, nothing beyond relatively rough astronomical measures can be expected in general. Modern instruments, capable of giving considerable refinement in terrestrial measures, are frequently not furnished with a striding level; and it is sometimes assumed, with the tacit approval of the makers, that such instruments are equally capable of giving refined astronomical results. On the older type of instrument a striding level—rarely not supplied—could have been, and sometimes was, extemporized; it seems as if ignorance of astronomy of position has led, at least in part, to the construction of theodolites in such a manner as actually to render such extemporization difficult.     

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.     

ADJUSTMENT OF SIMPLE FIGURES—II

Abstract

3. Adjustment of a Polygon.—The adjustment of a polygon by the method of the preceding paragraph leads to results similar to that for a quadrilateral, although not quite so simple, since there are two correlatives, k₁ k₂ , for deducing the corrections.     

A DRAFTING MACHINE FOR CIRCULAR ARCS OF ANY RADIUS

Abstract

1. Theory.—In Figs. 1. a and 1. b the letters R represent in each case four equal links of any length forming a freely jointed rhombus. L, L are two equal links of any length. (n ± 1), n are respectively a fixed and a rotating link whose lengths are in the ratio (n ± 1)/n.     

THE EAST AFRICAN ARC

Abstract

Choice of Beacon.—The general question as to whether luminous or opaque signals should be used in ruling triangulation has recently been discussed in the Empire Survey Review (No.9, pp. 151–2 and No. 12, pp. 335–6). It may here be summarized that opaque beacons of suitable design are sufficiently accurate and offer the considerable advantages of being immediately available for subsequent work, of requiring little or no attention, and of being visible from all directions without rearrangement. Moreover, if of the tripod or quadripod type, they need not be dismounted during occupation of the station for observing, so that 0bservations by more than one observer are not interrupted. The only occasion for using luminous beacons arises from bad visibility, whether through atmospheric haze or lack of a suitable background or through the economic necessity of completing observations at night. These conditions are not peculiar to ruling triangulation. An ”all-round” type of luminous beacon—a pressure oil lamp or a rotating mirror system—can be used for nightwork or against a dark background, but single-direction luminous beacons are necessary to overcome haze.     

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”.     

COMPENSATION AS A CONSEQUENCE OF TWO KINDS OF ROCK STRUCTURE

Abstract

The following points occurred to me when reading the interesting paper on crustal equilibrium in E.S.R. No. 23. The principle of compensation or isostasy necessarily involves the idea of two different kinds of rock structure—one strong, the other weak or in extreme cases fluid; for example, there is the familiar case of the strong iceberg resisting change of shape in the liquid sea. In dealing with crustal problems of the earth then, we should make up our minds which part is to be considered as strong, e.g. the granite crust, and which part as weak or fluid, e.g. material at a depth x km. (say roo km.); by weak or fluid I mean that a possibility exists of horizontal movement.     

A NOTE ON THE TRIGONOMETRICAL SURVEY OF SOUTHERN RHODESIA

Abstract

After the completion of Simms's Geodetic Chain in 1901 and the publication of the results in 1905—Volume iii of the Geodetic Survey of South Africa—nothing further of a geodetic nature was done until 1928 when a short chain was run westwards from Simms's chain, at about latitude 17° 10′, to fix the Copper Queen mining area. The Eastern Circuit was commenced shortly after this; it runs from Salisbury eastwards to the Portuguese Boundary, southwards through Umtali to about latitude 20° and then westwards, joining Simms's chain again to the east of Bulawayo. Another chain running north from Simms's work has been commenced near Bulawayo. The several series are exhibited on the outline map attached.     

ADJUSTMENT OF SIMPLE FIGURES: III

Abstract

5. Practical Example.—From Fig. 4 it is evident that the net of this example is made up of three polygons A, Band C, with no isolated triangles.     

A DIRECT METHOD OF TRANSFORMING RECTANGULAR COORDINATES FROM THE CASSINI PROJECTION TO THE GAUSS CONFORMAL PROJECTION

Abstract

6. Further Expansions.—Equations (4.3) and (5.5) enable a computer to transform coordinates from the Cassini projection to the Gauss projection without recourse to geographical coordinates. If applied to one or two points, no doubt these equations would be quite satisfactory; but if applied to 100,000 points their use would be laborious and it would be difficult to adapt them to machine computing.     

GEODETIC BEACONS

Abstract

Mr. Clendinning's article on “Signal Lamps” (E.S.R., vol. ii, pp. 15–18) raises a point of major importance in geodetic triangulation. I entirely agree with him that the sole use of heliographs—heliostats to the purist—is in most parts of the world out of date. I also think, and indeed am prepared to state categorically, that the use of acetylene lamps is out of date and was out of date many years ago. The Americans, who are always worth listening to on the economics of surveys, would not otherwise have replaced all their acetylene gear by electric beacons. The answer, in my experience, and for reasons which I shall endeavour to make clear, is generally, but not necessarily always, to provide both helio and electric lighting; but first I should like to summarize the conditions in which luminous signals should be used at all.     

SARAWAK LANDS AND SURVEYS DEPARTMENT: ANNUAL REPORT FOR 1935

Abstract

General.—During the year the Committee of Administration reviewed the policy and administration of the Department and recommended no change.     

SARAWAK LANDS AND SURVEY DEPARTMENT

Abstract

Financial.—The revenue collection for the year was 479,591.75, consisting of Lands and Survey Revenue 356,087.52 and Mining Revenue 123,504.23.     

TRAVERSING WITH THEODOLITE AND CHAIN

Abstract

As Mr H. F. Rainsford (E.S.R., no. 37, vol. v, July 1940) says, the ordinary accurate survey traverse, through its “ordinariness,” has been neglected in the printed word. The technique—perfected by much practice—has been handed down by word of mouth only from father to son, from surveyor to pupil.     

HIGHWAY TRANSITION CURVE DESIGN

Abstract

Any paper on transition curves would certainly be incomplete without the inclusion of a, section on the lemniscate, and whilst the writer personally prefers the Euler spiral as being easier to apply—once tables have beenprepared—it cannot be denied that within the range of tangential angle Φ used in ordinary highway practice, the two curves are so nearly alike in alignment that they must be equally satisfactory from the driver-vehicle point of view. The writer considers, however, that whilst users of the spiral generally seem to adopt a sort of "live and let live “attitude to the use of the lemniscate, exponents of the latter seem to have little good to say about the spiral. The main differences between the two curves are as follows:—(a) For the Euler spiral the intrinsio equation may be written lr = constant, whilst for the lemniscate the corresponding relationship is pr = constant, where p is the chord or polar ray AB in the writer's notation (see Fig. 1, p. 211). It follows from these two relationships that when the curves are flat as in the case of high speed spirals, the chord and arc-length are almost equal and the two curves must be almost identical also. It also follows, although not quite so obviously, that whilst the rate of change of curvature is exactly constant along the length of any Euler spiral, it eases off somewhat as a lemniscate gets sharper. This property will be mentioned again later.     

GRID BEARINGS AND DISTANCES ON THE CONICAL ORTHOMORPHIC PROJECTION

Abstract

Scale Correction Factor at a Point in Terms of X and Y.—Let dσ be a small line element of the curve ACB on the plane and ds the corresponding line element on the spheroid.     

SARAWAK LANDS AND SURVEY DEPARTMENT: ANNUAL REPORT FOR 1937

Abstract

General.—The excess of Revenue over Expenditure reached the unprecedented figure of 252,867; a net increase on 1936 of 23,018 in spite of a fall of 20,131 in Mining Revenue.     

SARAWAK LANDS AND SURVEY DEPARTMENT ANNUAL REPORT FOR 1936

Abstract

General.—The Surplus of Revenue over Expenditure was again a record, as the following figures show: 1933, 4,538;1934, 185,387; 1935, 196,669; 1936, 225,148.     

A NOTE ON ISLAMIC ASTRONOMY

Abstract

The splendid vista of exploration of the dark chasms of space recently opened up by the coming into full use of the 200-inch Hale telescope at Palomar, California (the instrument is really a giant camera) and the new technique of radio astronomy which has revealed the presence of “radio stars” (at present so called for want of a better name)—dark bodies whose precise nature is not yet determined—might lead some people to think that the work of the ancient astronomers and their immediate successors counted now for little. But to do so would be grossly unjust not only to the achievements of ancient Greek astronomy but also to the valuable legacy left to the Middle Ages by Islamic astronomy.