At present the total number of military and civil flights across the North Atlantic is about 130 per day counting both directions. Once aircraft are outside the systems of airways used in the high traffic density areas over each continent there are no fixed traffic lanes and aircraft plan their flights independently, generally following composite tracks to take maximum advantage of the wind distribution. Pilots are familiar with the natural tendency for tracks to diverge even when aircraft are being navigated via the same route but when the navigator in each aircraft is following an independent flight plan the separation of tracks will be much greater. Thus on the 2000-mile North Atlantic route the traffic density in real terms—say the number of aircraft per 10,000 square miles—is extremely low, and it is open to question whether the chance of two aircraft colliding in mid-Atlantic is not so remote as to be treated as an impossibility for practical purposes. This may sound heretical but if, as the writer suspects, the chance is so low as to make no significant difference to the overall risk of aircraft accidents, then there are other aspects of aircraft operation where the attention now being given to Atlantic traffic control might yield quicker dividends in the improvement of air safety.

In 1952 the Institute set up a Working Party, under the chairmanship of Mr. D. H. Sadler, to investigate the accuracy attained in the practice of astronomical navigation at sea. The report that follows was presented in summary to the Technical Committee on 15 February, 1957, and formed the subject of a discussion at the Institute's meeting on 21 June.

The following conclusions relate to a total of 424c, observations received by the Working Party from 173 observers, and are representative of navigational practice as a whole only in so far as the observations, and the observers, are so representative. Only 3319 observations from 1 r6 observers were retained as suitable for analysis, and in nearly half of these observations the ship's position is not known sufficiently accurately for them to be included in the main analysis.

When, last year, you elected me to be your President, you placed upon me the duty of delivering before the Institute the tenth Presidential Address. My predecessors in this office have been men of considerable scientific and administrative distinction, able to talk with authority in their respective fields of learning. I, however, come before you mainly as a practitioner of air navigation, the first such to be your President, concerned with the practical business of ‘how to get there’ in an imperfect, and only partly understood, world, rather than with the elegant demonstrations of a theoretical technology. The duty of preparing a Presidential Address, though onerous, has its compensations. It is the one occasion in the Institute's year when a speaker has the right to stand up before you, and to muse and speculate on controversial matters, rather than to present an account of completed work. A recent writer speculating on the future growth of air transport took as his motto: ‘Behold the turtle—she advances only by sticking her neck out’. This is true not only of turtles, but exemplifies the spirit which is needed to meet the challenge of the future: it is in such a spirit that I offer this Address.

One of the problems in arctic navigation by astro is the twilight period. At this time, if the Moon is below the horizon, suitable objects for sextant observation are not easy to find. The difficulty is aggravated by the fact that on certain flight paths the arctic twilight may last for many hours. It must also be remembered that in these areas the behaviour of the magnetic compass and of radio aids are often unreliable and this increases the relative importance of astro-navigation. With the introduction of the periscopic sextant into air navigation it has become possible to pre-set the instrument for a given star or planet and satisfactory observations may be possible when the heavenly body is still below the level of casual perception for the unaided eye. In this connection it is necessary to know what stars are likely to be seen under twilight conditions if efficient flight-planning is to be carried out.

Of the many factors affecting the collision problem, the mathematics of relative motion is the one most susceptible to formal analysis. Moreover, this ‘collision geometry’ must form the basis of any investigation into the instrumental, operational and human factors involved. It is therefore surprising that no complete description of the (mathematically) simple relationships is readily available. The object of this paper is to present such a connected account of the mathematics of relative motion, in so far as it appears relevant to the collision problem and within the limitations of time and space available.

The objects of the International Geophysical Year have been fully described in the Journal. The idea itself was first conceived in 1950 at a social gathering in the home of Professor J. A. van Allen, in Maryland, U.S.A. The small group included Professor Sydney Chapman of Great Britain and Dr. Lloyd Berkner of U.S.A., now respectively the President and Vice-President of the special committee for the International Geophysical Year. They considered that recent advances in geophysical science were such that an interval of fifty years, such as lay between the First and Second Polar years, would be too long. Moreover an interval of twenty-five years from the Second Polar Year would coincide with a period of maximum sunspot activity. Later in the same year the International Council of Scientific Unions adopted the idea and in the following year set up the special committee; at the same time the nations adhering to I.C.S.U. were invited to form national committees, of which there are now more than sixty. Their programmes make up the vast international world-wide effort. A duration of eighteen months, July 1957 to December 1958, for the Year was agreed.

There are still people who believe that only during the last four-hundred years have we known that the Earth is a globe. They were taught this at school when they were told the story of Christopher Columbus. Columbus, it was said, went to King John of Portugal with the proposal to reach the fabulously rich Cathay, situated in the Far East, by sailing across the Atlantic Ocean to the west. The king consulted a committee of mathematicians who rejected the idea with scorn. The Earth was round and flat like a trencher, they said, and not a globe as Columbus maintained. And some teachers added that not until the circumnavigation of Magellan's ship, Victoria, was there any proof of the shape of the Earth.

At the present time with the increase of air traffic across the Atlantic (and still more so in the future when jet aircraft will be numerous) it becomes very necessary to know what is the safe separation between aircraft, and whether some form of controlled paths may not economically be imposed between America and Europe.

The question is being asked more and more, why, despite the use of radar, collisions at sea in fog still occur. There are evidently many answers to this question and all or nearly all of them hinge on some aspect or other of human fallibility. Yet these answers may be grouped into two distinct categories, one of which covers failure to get the most out of the radar and ancillary equipment, and the other the problems of behaviour with which the radar information brings the mariner face to face in fog for the first time.

In 1874, the Austrian arctic scientist, Weyprecht, on his return from an Austro-Hungarian polar expedition stated that, though many countries had sent expeditions into the polar regions at great expense and involving appreciable hazards to those participating, no important contributions to knowledge had resulted from them. They had done a certain amount of mapping and obtained a few meteorological observations but the primary object had been, as a matter of national prestige, to plant the flag nearer to the Pole than had been reached before. In his opinion what was needed for the advancement of knowledge about the polar regions was that nations should collaborate in sending expeditions to various parts of the arctic region to make observations throughout the whole of one year. Largely because of his persistent advocacy of this view, the value of the proposal came to be recognized, and as a result the enterprise known as the First International Polar Year was developed. A number of countries combined to send expeditions to establish observing stations at selected points in the arctic region to make observations throughout the year 1882–3 in meteorology and geomagnetism and also of the aurora. The observations made during this Polar Year contributed appreciably to knowledge of geomagnetism and of meteorology.

The pattern of port operation in fog which was established in Liverpool in 1948 when the Port Radar Station (Fig. 1)was opened, has not materially altered, except in the volume of shipping now using the service provided.

A straightforward shore-based radar has been shown to be a reliable and effective aid to pilots in bringing ships in from sea in fog through the port channel area into the berthing area, with or without the assistance of the ships' own radar. Once there, however, further movement now depends upon the visibility in relation to such factors as radar assistance, shipping density, the presence or absence of emergency anchorage, the nature of the berth, that is, floating stage, river wharf, or dock, and so on. Below a certain visibility, shipping hold-ups and increased risk of stranding for ships on the move may be expected, As an ultimate ideal, we may have in mind the integration of all available facilities and inventions so as to allow shipping to carry out all its normal activities in the worst of fogs, with no less speed and safety than is customary in clear weather. But this is rather idealistic, and I would like to introduce a criterion, suggested by Mr. Eric Parker, which he terms the ‘Critical Visibility’, and which is the visibility at which 50 per cent of ships will proceed no further than the berthing area. This statistical measure of the effect of fog is one which will give a real indication of the value of any improvements. It will of course be different in different ports, but if say it is half-a-mile with no shore radar assistance, the introduction of shore radar might reduce it to quarter-of-a-mile, and in a few years time it might be reduced by improved aids to say a hundred yards. Eventually it would be at such a value that annual delays to shipping would be of negligible importance.

If navigation were confined to the function of keeping a craft on a desired track, and estimating its progress periodically, then a long-range turboprop would present no features of navigational interest. Navigation, however, is supposed to encompass a wider field than this. In a famous sixteenth-century definition, ‘Navigation demonstrateth how, by the shortest good way, by the aptest direction, and in the shortest time, a sufficient ship between any two places may be conducted’. The economic realities of modern airliner operation give a new emphasis to those phrases ‘By the shortest good way, by the aptest direction, and in the shortest time’. A Britannia 310, for example, which will be the first, probably the cheapest, and possibly the smallest, long-range turbineengined airliner, costs about £1 million and is capable of producing a gross revenue of £1000 per hour. The sum of payload and fuel load is limited in most long-range cases by maximum take-off weight, and the fuel for one hour of flight is equivalent in weight to about 2 5 passengers and their baggage. It is not surprising in the circumstances that quite minor refinements of navigational technique are worth tens of thousands of pounds per aircraft per year, while major improvements can alter the status of an aircraft type as an instrument of transport. Such aircraft should be considered as acutely sensitive instruments to be operated precisely according to scientifically designed techniques.

Some meteorological offices now include isotachs (lines joining points of equal wind speed) on forecast upper-air charts for long-range flights. Heretofore, dispatchers and aircrews have been obliged to measure winds from upper-air charts displaying contours only. This meant use of a geostrophic wind template, and correction for cyclostrophic component and latitude. The new contour-isotach charts, in addition to displaying wind speeds more readily, present greater accuracy, since they are determined by forecasters, who may call upon better theoretical know-how, and later observational data. In order to take full advantage of this improvement, Trans-Canada Air Lines has developed two new templates; one for route analysis (determination of the best-time track) and the other for flight planning. These are designed with ease of production in mind as well as simplicity in use. They are produced photographically on heavy film, and have no moving parts.

In view of the immensity of the sea, the relative smallness of ships and the range of speeds, the probability of a collision at sea between ships blindly following constant and random courses is very low. Even on high-density routes, the probability is low for intersecting courses if speeds and headings remain constant. The risk is higher for routes which are at angles of less than 20° from each other, and where a ship is overtaking another rather than following an opposite course. It is lower if the speeds are very different, and higher if they are similar.

This paper was presented by Captain Wylie at the Full Assembly meeting of the Radio Technical Commission for Marine Services in New York on 26 October 1956. The subject is dealt with under three headings: Communication, Navigation and Anti-collision.

To the landsman of the western world, telecommunication is as unremarkable a part of his life as his toothbrush. To the seaman in the old tradition, it may occasionally be anathema, but to the modern mariner that feeling of isolation which came when the last mail had been collected and the shore telephone line disconnected, while sometimes a blessed relief, is becoming an anachronism. On shore, the use of the telegraph service has receded very greatly as a result of the increasing efficiency and availability of the telephone. More and more people discover and insist upon the advantage of personal contact by speech. At sea there is little difference in the desire, but a great deal in its gratification, due to lack of facilities and to failure to provide an integrated system which will serve the ship from mid-ocean to her anchor berth in port.

The advent of true-motion radar has been a great step forward in the problem of allowing a ship to operate safely in congested waterways. Harbour radar, however, is still a requirement for two reasons; first of all it can well provide far more immediate information than is available from true-motion radar. Fig. 1 emphasizes this by showing how much additional information can only be available directly from a static site. Consequently it allows shore authorities to be advised of what is happening in conditions of bad visibility where they would otherwise be devoid of most information. This raises the problem of how the information is to be used.