During 1943 there was produced, for trial purposes, a limited edition of the so-called Experimental Astronomical Navigation Tables (E.A.N.T.s). For various reasons these tables were not adopted for general service use in the Royal Air Force, and copies are no longer available. The tables possess some points of interest, which are described below for the first time.

Ever since you did me the honour of making me your President it has been fairly inevitable that the subject of today's Address should connect the work of hydrographers with that of navigators. It has also been clear to me that I should not try to emulate too closely the two distinguished men of science who have been my predecessors in office. Their Addresses have contemplated, and given us useful thoughts for, the future; mine will be more easily developed from the standpoint of the user, and will attempt to see how accepted principles and methods are in fact being applied for the navigator's purposes.

The choice of airspeed and altitude have a far more critical effect on economy of operation throughout the flight of turbo-jet aircraft than with the piston-engined type. The method of operating piston-engined aircraft for maximum range is well known, though it is normally only used on very long stages when fuel is critical; generally constant-power or constant-airspeed cruising, which result in a small penalty of fuel or payload, are preferred. The choice of operating height is also fairly wide within certain obvious limits. With jet aircraft, however, airspeed and operating height become critical and variations from economic operation reduce the payload or range considerably. The preparation of the flight plan, involving the choice of cruising altitude and speed, therefore becomes of major importance to the jet operator and navigator. The guidance of the aircraft's flight path in the vertical plane, in other words, takes on a new significance and affects the navigator's task both in planning and in flight.

The need for investigations into the detection of ice by radar became apparent when merchant ships started reporting that ice formations were inconsistent radar targets, and that ships relying upon radar to navigate through ice areas could, in some circumstances, have their safety endangered.

Certain investigations, notably those carried out by the U.S. Coast-guard Service and by the Swedish Defence Research Institute, resulted in the publication of a great deal of useful descriptive information but it was not accompanied by measurements of the actual echoing power of ice targets. With the object of carrying the matter further, a special enquiry was made during the 1950 and 1951 North Atlantic ice seasons, when a number of British ships plying North Atlantic routes completed questionnaires in which the sizes and shapes of ice formations were noted together with their radar detection ranges. This enquiry was instituted by the Operational Research Group in the Marine (Navigational Aids) Division of the British Ministry of Transport, which later analysed the data collected and issued a report. There were, however, certain limitations in this investigation. For example, the performance of the radars was not known, because of their inherent differences and the fact that none of the ships carried instruments, such as echo-boxes, for checking performance; further, propagation conditions at the time of making the observations were not established.

In an earlier paper it was suggested that developments in air navigation had created a requirement for a new form of air plotting chart. The chart illustrating the present paper was produced experimentally by one of the airlines to fulfil this requirement. The main factors taken into account in designing the chart were as follows:

(i) The air navigator is always working against time. He therefore requires his plotting chart to show as much navigational information as possible, so that he need not spend time looking things up in books or transferring information from other charts.

(ii) The scale must be limited by the requirement for easy handling in the cockpit, especially when the chart is intended for use in aircraft that have no navigation table.

(iii) The design of a chart that has to show as much information as possible on a small scale is chiefly a problem of avoiding congestion. The items that might be shown therefore require careful consideration and only those that make a justifiable contribution to the chart's navigational purpose should be included.

(iv) When flying under visual flight rules (VFR) the navigator's problems are less acute than under instrument flight rules (IFR). The chart should therefore be designed for IFR; it will always be adequate for the easier case of VFR.

Upper winds over the North Atlantic are strong and their circulation is complex; until aircraft speeds are considerably increased, therefore, the choice of a route which will take the maximum advantage of the wind distribution consistent with safety can make a worthwhile contribution to operating economy. This paper describes some of the methods adopted by Trans-Canada Airline on its North Atlantic route to achieve this end.

Aircraft such as the Comet normally fly above cloud formations, but their approach to the airport involves a long and more or less gradual descent which may take them through adverse weather conditions. Violent thunderstorms, for example, which are fairly common in some parts of the tropics, constitute an obvious danger, and the provision at airports of an effective system of cloud warning could provide an added measure of safety along air routes.

In a previous article in this Journal mention was made of an unexamined manuscript by Hariot belonging to the Petworth Collection entitled The Doctrine of Nauticall Triangles Compendious, which promised to be of interest to navigators. When Lord Leconfield, the owner of the Collection, heard of this he very kindly himself brought this manuscript to the British Museum for study there, and meanwhile Dr. Shirley of the United States, who is at work on other aspects of Hariot's life, sent over from America a transcript from a microfilm copy which was in his possession. The contents of the manuscript more than fulfilled expectation, for it appeared that the main theme was the computation of meridional parts for drawing a Mercator chart and, as Mr. Sadler, the Superintendent of H.M. Nautical Almanac Office, shows in the second part of this paper, Hariot was remarkably in advance of his time in his mathematical treatment of this problem, which continued to be a favourite one for discussion until the discovery of the calculus. As is well known, the first table of meridional parts to be published was that compiled (by simple addition of secants) by Edward Wright (1558–1615) of Caius College, Cambridge, a mathematician who had been nautical adviser to the Earl of Cumberland, and on occasion to the Lord High Admiral himself.

In view of the appeal for observations that has been issued by the Institute to assist in the determination of the accuracy of astronomical observations at sea, it may be of interest to navigators to recount some of the experiences of a hydrographic surveyor. Large regular surveys usually depend on geographical positions which are obtained on shore with accurate instruments. In cases where surveyors fix these positions with astrolabes, or occasionally theodolites, three observers will probably have taken observations of some thirty-two stars each. In the analysis, intercepts of the order of 4–6” are obtained, and the final position is probably accurate to about 1”. Some hydrographic surveying, such as a one-day search for a reported shoal out of sight of land, various minelaying and minesweeping operations out at sea, and the determination of oceanographical stations on long passages, however, demand ordinary sights taken in the normal way at sea. The value of the hydrographic operation may depend on the accuracy of these sights, and therefore the report on the operation generally attempts some assessment of their accuracy. Considerable care is taken to achieve accuracy and often the ship is stopped and the sights referred by range and bearing to a moored beacon, even in depths of 500 fathoms. Methods of determining the accuracy obtained may be by taut-wire runs from known points of land or taut-wire distances interconnecting several beacons. Failing, or in addition to, these methods, two to four observers' results may be compared, or Sun and star sights can be referred to the same beacon; even short tautwire or patent-log runs to well-defined and previously well-fixed fathom lines have been used.

The problem of navigation in high latitudes is becoming increasingly important as the range of modern aircraft increases and the consequent inevitability of the extension of possible operational theatres to include polar regions becomes apparent. The provision of suitable maps of such areas is therefore a matter requiring attention in the near future, and the adoption of a standard projection together with uniformity of presentation of topographical detail must be regarded as a desirable objective in this connection. The aim of this paper is briefly to review and compare the various projections available and so assess which one is most suitable for the purpose.

The new U.S. Hydrographic Office publication H.O. 249, Sight Reduction Tables for Air Navigation, comprises three volumes: Volume I covers all latitudes and contains tables of altitude and azimuth of selected navigational stars; Volume II contains tables of computed altitude and azimuth angle for latitudes 0°–39°, declinations 0°–29°; and Volume III contains tables of computed altitude and azimuth angle for latitudes 40°–89°, declinations 0°–29°. The tables have been produced jointly by the American Nautical Almanac Office and H.M. Nautical Almanac Office for the U.S. Hydrographic Office. The British edition of the tables is being published by H.M. Stationery Office as A.P. (Air Publication) 3270; the actual tables are identical with the American edition but the introductory matter has been reset.

As Professor Taylor has described, the Hariot ms. is largely concerned with the calculation of meridional parts. These calculations are of great interest not only as regards the question of priority, but also because they are based on a method which was more than fifty years in advance of contemporary mathematical knowledge. Although the ms. is paged and cross-referenced, the calculations are incomplete and inadequately explained; arithmetical errors (remarkably few when all calculations had to be done by long multiplication!) make absolute interpretation of all figures almost impossible. Considerable detail is thus unavoidable if the essential parts of the ms. are to be put on record and explained; though the most important point must be left unexplained. There can be little doubt that Hariot's calculations are original and independent.

Although the Astrograph has never been formally described in print, the basic principles of the instrument are sufficiently well known to require no further elaboration; so also are its limitations. Over many years, numerous proposals (but mainly unpublished) have been made for the extension of the Astrograph to cater for the Sun, Moon, and planets, as well as for a larger number of stars, but none have been really satisfactory. Without such improvements the Astrograph must have a very limited use, and accordingly a further study was made some time ago of its application to the Sun, Moon, and planets. Methods were developed on familiar lines for shifting (and rotating) the star curves for a standard declination to cater for neighbouring declinations, but these introduced complexities that were clearly unacceptable.

The library of the Royal Geographical Society contains a great many early charts and works on navigation which will be of interest to members of the Institute. Mr. Crone, the Society's Librarian and Map Curator, describes some of them in this paper, which deals in the main with publications likely to have been used or referred to by practising navigators. Arrangements can be made for members to inspect works in the Society's collection.

During the last half-century authors who have had occasion to write about the history of the magnetic compass have quoted extensively from The Intellectual Rise in Electricity, by Park Benjamin (New York, 1895). The wealth of references given by this writer to substantiate his statements promises a reliability which is at times sadly lacking. In one part of this book the statement is made that: ‘A single Finnish Compass has been discovered for which the people claim great antiquity, the card or scale of which is marked for a latitude where the sunrise and sunset at the summer and winter solstices differ by sixty degrees.’ For this the author gives as authority Nouvelles Annales des Voyages, Vol. xvii, page 414 (Paris, 1823), but in fact this reference contains no suggestion of the discovery of an ancient Finnish compass. All there is, is a brief reference to the ancient Finnish method of dividing the compass card which, instead of four cardinal points, had six, spaced sixty degrees apart. This information was said to be based on an article in a monthly miscellany, published in Finland under the name of Mnemosyne. Captain D. Daragan of Helsinki has been kind enough to obtain for me a copy of the original article, which was printed in Swedish, and Rektor S. Nydell has been so good as to translate it into English.

It is now seven years since the first R.A.F. polar flight was carried out by Aries, a Lancastrian aircraft from the Empire Air Navigation School; during that period air operations in Arctic regions have become an every day occurrence. This paper describes a series of flights undertaken recently by the Royal Air Force Flying College; it is not intended as a discussion of the special techniques of navigation in high latitudes but merely as an illustration of their application in a typical case.

More research into fuel reserve policy needs to be done if airlines are to achieve the finest balance between payload and safety. Progress is required in the accuracy of weather forecasting, in streamlining the techniques associated with the choice of required fuel reserves, and in research into the greater benefits that could be derived from well-developed operational control policies, exploiting to the full the enormous potentialities of a system-wide communications network. Captain Moline has suggested some of the inadequacies of present-day techniques.

There are two stages in the determination of position from current observations. The observations are first resolved into positional form on the chart and plotted so as to give either a fix or a position line. When more than two position lines are available, some of the information is redundant and a problem exists of determining the most likely fix. In the case of air navigation, the number of position lines seldom exceeds three, and the determination of position in this case has been studied in a previous article.