The sailor will not be kept from the sea, even though empires fall and foreign invaders multiply. Yet we cannot expect to hear much of him in such troubled times. We know, however, that although European ships no longer sailed to India, yet, after the barbarian destruction of the Roman Empire, overseas trade did revive, and the foundations of such famous maritime states as Venice were laid. We know, too, that although the Arabs overran the whole length of the Mediterranean Sea, they were pushed back out of the islands by sea-borne expeditions from Italy and Catalan Spain, while when the Holy Places in Palestine were captured by the Turks (who were not ‘gentlemen’ like the Arabs), there were ships and sailors ready and able to carry crusading armies to the East, and to provision them while they were there.

The problem of navigation, reduced to its very simplest terms, is how to get from X to Y. But this statement appears at first sight to require the proviso ‘given the means of transport available’, whether camel, ship, plane or rocket. Each sets up its special limitations to free movement, but in effect merely determines that XY must be broken up into segments, X Y1, Y1 Y2 and so on. Further reflection would probably add two additional considerations, the navigator must get safely and expeditiously from X to Y. But this again can only break down the route into fresh segments whereby dangers and difficulties are avoided. It is still for the navigator just the problem of getting from X, where he is, to a designated Y, where he wishes to be.

How did Francis Drake navigate his ship when in 1577 he embarked upon his famous voyage round the world ? Strictly speaking he did not navigate her, for the task was delegated to subordinate officers. The Pelican (or Golden Hind as she was later renamed) carried, as was customary, a master and a pilot whose duty it was to make the necessary observations and lay the ship upon her course. But these had signed on for a supposed voyage to Alexandria to load currants, and Drake knew well enough that no English pilot could then compare with a pilot of Spain or Portugal, whether in training, experience or equipment: for these nations, as pioneers of the Great Discoveries, had also taken the lead in the development of nautical science and in the formal schooling of seamen. That explains why Captain Francis furnished himself with the latest chart from Lisbon, and why, when he reached African waters, he kidnapped a Portuguese pilo to sail him into the Pacific, only to maroon the unfortunate man in Central America when he had served his turn and a Spaniard was indicated for the next stage of the voyage. Hitherto no English ship had left the Atlantic, and apart from a few men trained in the Muscovy Company's service the average English sailor laughed at the idea of navigating with charts and instruments. He had his compass, he knew his landmarks, and once he was in soundings he could cast the lead and feel his way into harbour blindfold. To see a man ‘shooting the Sun’ (as it was already termed) with a cross-staff was an occasion for mockery. ‘Have you strook it?’ he would cry, ‘Have you strook it?’ And as for charts, he wanted none of your sheepskins, he could make his voyage as well upon a board! It was upon a prepared sheepskin that the mediaeval charts were drawn and painted, the neck to the left, while the ‘board’ was the traverse-board marked with the thirty-two rhumbs. These were pierced with holes at regular intervals, into which pegs were inserted at each turn of the sand-glass, thus recording the time sailed on any particular point of the compass.

The institute of navigation has been formed to promote the interests of science and of practical navigation, by uniting together in a scientific body those who are concerned with or are interested in the science and art of navigation. For navigation is both a science and an art, whose development must be based upon the knowledge and experience of many different types of persons. The formation of the Institute was stimulated by the formation in 1945 in the United States of an Institute with the same aims; it is likely that similar Institutes will be formed in other countries also. Arrangements are in hand whereby the members of either the British or the American Institute will have the privileges of both, and it is planned to form an international committee to co-ordinate the work of the various separate Institutes. In navigation, as in other branches of science, there is much to be gained by international co-ordination and co-operation.

The rotation of the Earth provides the ultimate standard of time. As the fundamental unit of time we can use either the mean solar day or the sidereal day; these two units are related in a definite manner, so that when one is determined, the other can be inferred. The purpose of any timepiece is to subdivide the day into shorter intervals, and so give the time at any instant. No timepiece will give exact time; the error of the timepiece at some definite instant and the rate of change of that error, or, briefly, the rate, must be determined in order to extrapolate for the correct time at some subsequent instant. The accuracy of the extrapolation will depend upon the uniformity of the rate of the timepiece. Radio time signals sent out from an observatory, which is responsible for the determination and distribution of time, provide the most convenient means for deriving the error and rate of a timepiece. For normal navigational purposes an accuracy of about 0·05 seconds is adequate. But for the purpose of frequency control a very much higher precision is needed—but a precision in time interval rather than in absolute time. Some of the radio-aids to navigation depend upon the accuracy in standardization of frequency, so that high accuracy in time interval has become, indirectly, a navigational requirement.

This paper is concerned with two different problems. The first of these is to correct a magnetic compass so that the essential relationships for zero deviation are maintained even when the ship rolls and pitches. The Harvey-Raynes corrector is described and its advantages are explained. This corrector makes it possible to steady the compass at any time without affecting the accuracy of the existing deviation card.

The second problem considered is the automatic correction of deviation for transmitting magnetic compasses. A system of ‘point-by-point’ correction is developed, based upon the representation of the deviating force by a truncated Fourier series; it is shown that such a truncated series may be represented mathematically in a form immediately suitable for practical application, some such forms being described in detail. It is shown that by means of a small additional device the ‘point-by-point’ type of corrector may be made to correct both variation and deviation, so that for any given part of the Earth the transmitting magnetic compass may be made to point true north.

The design of an almanac is a highly technical matter in which principles may have to yield to practical detail. In order that the proposals shall be fully appreciated and fairly discussed the basic principles that have led to the present proposals, and their practical alternatives, will be indicated as briefly and as objectively as possible.

In the Nautical Almanac Office we have much experience in the presentation of astronomical and numerical data; but we are not navigators and we have little experience of the practical use of the Abridged Nautical Almanac. While all criticisms will be welcomed, those relating to practical requirements will therefore be particularly valuable.

The foundation of the Institute of Navigation has given satisfaction to many, but perhaps to none more than the shade of the great man who in 1673 inaugurated on the basis of the old charitable institution of Christ's Hospital ‘a nursery of children to be educated in Mathematics for the particular use and service of navigation’. That science has made some strides since Samuel Pepys's day. But no one who has read Arthur Bryant's fascinating study of the Great Secretary of the Admiralty under the Restoration can doubt that old Samuel would have been well abreast, if not ahead, of all developments, especially as they affected the King's Fighting Services. His comments on the subject after his experience of the Great Storm of 1684 have a very realistic and modern ring about them: ‘We are very solicitous in our disputes and opinions touching our draughts and log lines and things’ he wrote ‘when we are at a loss for our ways … but as soon as ever we see land all difference is forgot, or any desire of recording the truth, but on the contrary, everybody endeavours to make himself be thought to have been in the right, and not thinking also that they should ever come to the same loss in the same place again. Hence it comes that the science of navigation lies so long without more improvement’. How true, and how curious that it should have been more than 260 years before the foundation of this Institute, under a president one of whose predecessors was called in by Pepys in 1686 to defend against unjust criticism a treatise on the science of navigation.

The scientific world will warmly welcome the foundation of the Institute of Navigation, and indeed we may regret that it was not founded long ago. The interest in scientific navigation goes back nearly 300 years, since it was with the aim of assisting navigation that the Royal Observatory was founded, and during the eighteenth century navigation was greatly advanced by the encouragement given to Harrison in his work on the chronometer. It took some time before this was extensively used at sea, but by the beginning of the nineteenth century it would have appeared that astronomical navigation had nearly reached perfection. It was a fine and accurate science, as witnessed by the world surveys made by such seamen as Captain Fitzroy in the 1820's and 1830's, and little more seemed to be called for, or indeed could be expected as long as astronomy was the sole means of location. In the seventeenth and eighteenth centuries our Institute would have had a great many interesting activities, but in the nineteenth we cannot help feeling it would have been rather dull. Even then, however, there is a matter that may excite our surprise, for the ‘Sumner’ line was discovered at a rather late date, by a master mariner at sea, whereas it ought to have been an obvious idea to anyone with even a rudimentary mathematical training.

The paper is divided into two parts.

Part 1, under the heading of Non-standard Propagation, concerns variations in the apparent performance of marine navigational radar in its use for detecting shipping and land targets. The effects of changes in the density of the lower layers of the atmosphere on radar transmissions, their distortion of radar coverage for better or for worse, and resultant errors in the evaluation of echoes are here examined.

Part 2 describes the way in which weather echoes may influence and restrict radar-assisted navigation. The attenuation of field strength with various types and intensities of precipitation, and the effects of these factors on the navigational and collision-warning uses of radar are examined. The detection, tracking, and application of weather echoes as an aid to short-range weather forecasting are also covered.

A Brief introduction on the purpose of the paper constitutes Part 1.

Part 2 of the paper traces' the historical development of navigational radar in the United Kingdom from the beginning of the late war to the present day. The use that was made of the very early radars is mentioned and the improvement brought about by the introduction of the PPI and centimetre radar is described. An account is given of how radar assisted the Normandy landings, of the techniques employed and the lessons that were learned. It is shown how a change to shorter wavelengths improved the performance, and how this made possible a large experiment in the Scheldt Estuary designed to help convoys to reach Antwerp in fog; the navigational difficulties of this experiment are described and it is shown how an elaborate drill had to be prepared for navigating these difficult channels to allow the troubles to be overcome. The thought that was devoted to the navigational needs of the Merchant Service in peacetime is dealt with, together with the elaborate trials that were carried out in the Thames Estuary to check the plans for peacetime development. It is shown how the new equipments which were developed brought about a large improvement in performance and ease of operation. In particular, the use of new displays allowing the PPI to be superimposed on the chart is dealt with and the simplification of navigation and pilotage which this allowed; the success with which ships were navigated and piloted on radar information alone is also dealt with. Some notes are included on the work of the two first International Meetings on Radio Aids to Marine Navigation. A short account is given of some experiences with radar in Norwegian Fjords.

Part 3 describes the present position where commercial navigational radars are in production and fitted to a number of British and foreign vessels. This part compares the performance of some British and United States equipments and also compares the requirements of the British and United States Government performance specifications.

Part 4 reviews some of the problems outstanding today and makes some suggestions on possible future developments. In particular, suggestions are offered on improved PPI'S, on new systems of chart comparison, on an alternative form of display for ship-handling and, looking rather further ahead, on a new form of close range and pilotage radar.

The purpose of this lecture is to review briefly the many methods at present available for the reduction of astronomical observations, and to make suggestions for the future. The main conclusion will be that altitude-azimuth tables provide the simplest and quickest method of reducing a sight.

It should be made clear that this is not a comprehensive survey setting out to examine and criticize every method; the bibliography of papers and tables (itself incomplete) published by H. Bencker in The Hydrographic Review, which contains some 1200 references, indicates that such a task would demand months of research. Attention is directed towards the principles of the various methods, and the limitations of each principle are discussed independently of the actual tables existing for the application of the method.

The objectives of navigation have, in the special case of air services, been summed up, in an ‘R.S.V.P.’ formula, as Regularity, Safety, Versatility and Punctuality. The formula holds for all navigation, since the object of every operator and every master is to carry his passenger or freight in safety on a preconceived time schedule, with virtually complete freedom of choice, by owner or master, of type of craft, of time of departure and of route. The enemies of this freedom of choice and of the preconceived schedule are almost wholly meteorological or astronomical; the only serious enemies are meteorological. The continuing concern of the ‘navigator’ proper is to avoid, detect and rectify departures from the preselected route and schedule. The whole task of ‘navigation’ is unfulfilled without an infallible look-out for dangerous obstacles, which may be at fixed and known absolute positions, or at random, variable and unknown positions relative to the craft. Good ‘eyes’ naturally or artificially aided and a good clock would be the only indispensable tools of whole navigation, were it not for those imperfections of the science and art of weather forecasting which leave the drift term in dead reckoning such a deplorably variable and unmanageable element in the dual problem of the navigator. That dual problem is ‘Where am I now?’ and ‘Where shall I be in x minutes from now?’ The unpredictability of the drift term and the imperfections of the navigator and his instruments prevent the answer to the second question emerging mechanically from the answers to the two much simpler and essentially similar questions: ‘Where am I now?’ and ‘Where was I y minutes ago?’

Almost ten years ago (14 March 1938), in this same lecture hall, the Astronomer Royal, our newly elected President, opened a discussion on the recently published Air Almanac. That meeting, held under the auspices of the Royal Geographical Society, can justly be said to mark an epoch in the application of astronomical methods to air navigation in this country; but it was remarkable in other ways too. First, it provided that opportunity for criticism, by users and by others interested, of the provision to be made for astronomical navigation in the air, which it is hoped the Institute will provide for all aids to navigation. Secondly, the preparation of the Astronomical Navigation Tables was first announced; this may not appear very remarkable in itself, but it was the first time, since the days of Nevil Maskelyne, fifth Astronomer Royal, that the Nautical Almanac Office had prepared any major tables for the reduction of navigational observations!

The basic principles of Consol have been explained in a previous article; the factors affecting the range and accuracy of the system are here discussed. A summary is given of the results obtained practice, and the article concludes with a brief discussion of developments which will lead to improved performance.

The questionnaire shown below was circulated to all members of the Institute. In the following analysis of the replies, forms completed by members with no experience or direct concern with surface navigation have been disregarded. The substance of replies received from members in the Royal Navy has been given separately. It has not been possible to detect any marked unanimity in the answers given by Examiners, Navigation School instructors, Marine Superintendents,&c., and these have been included under the heading of Merchant Navy.

The detailed comment given is taken from the discussion at the Meeting and from letters and memoranda sent in to the Institute. In some cases it refers (e.g. layout, &c.) to matter not reproduced in the Journal. For convenience of reading reference numbers have been given to the authors of comment.

Some apology, or at least an adequate excuse, is needed for resurrecting a theoretical treatment of the effect of coriolis acceleration on observations of altitude made with a bubble sextant. Such an excuse is provided by the recent publication by Dr. J. J. Green of an article suggesting that the correction table (Z-correction) given in both the British and American Air Almanacs (and in many other Air Almanacs) is incomplete. In a reasoned letter to the Editor of Navigation, Dr. G. M. Clemence, Director of the American Nautical Almanac Office, has given a simple and straightforward explanation of the two separate and distinct causes for the deviation of the zenith as indicated by the bubble of a bubble sextant; and he has further justified the present practice adopted in the almanacs. Considerable interest has, however, been aroused and it seems opportune to give a previously unpublished general derivation of the theoretical correction, together with a brief discussion of the difficulties of practical application.

During the course of the Second World War, consideration was given to the means for operating post-war air routes. Concurrently, discussions were taking place as to the type and performance of the aircraft likely to be available. It was, however, quite obvious that, as we had had no previous experience at the higher altitudes at which these operations would be carried out, account would have to be taken of the winds which would be experienced, and steps were taken therefore to procure these data whereby to plan the routes.

The principles of radar-meteorology have been described by Lieutenant Satow in his paper. This note contributed by the Technical Secretary suggests a system for the collection of data from which a statistical evaluation of one aspect of the subject may be made. Bound copies of this paper with 25 log sheets may be obtained on application to the Institute, price 1s. 6d.—Editor.

The paper discusses the way in which the accuracy provided by different navigation systems can best be presented diagrammatically, and it is concluded that contours of constant 95% radial error give the best general picture of a system. Where a more detailed picture is required error ellipses can be added at suitable points in the system. The 95% radial error of fixing is calculated for radial, rθ, azimuthal and different hyperbolic systems, and graphical methods are developed for drawing contours along which the 95% error is constant, and also for drawing 95% ellipses. Diagrams show typical results for the different systems.