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.

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.

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.

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.

A study of many collisions at sea in which the misuse of radar may have been a contributory cause leads to the conclusion that much difficulty might be overcome if a less ambiguous method of displaying radar information were provided. To this end an entirely new type of radar presentation has been embodied in the latest equipment produced by Decca Radar Limited. Type TM 46 displays the radar picture so that the true movements of all vessels, including own ship, can be assessed by inspection of the display. This continuous presentation on the radar screen of the true course and speed of all targets is an entirely new feature in radar equipments. Unlike former systems, where own ship appears continuously at the centre of the display and the movement of other echoes is relative, ‘true-motion’ presentation shows own ship moving across the display at the correct course and speed, and the true movement of other echoes. Stationary objects such as buoys or anchored ships do not move on the PPI and can be readily identified.

The invention of the balloon was almost a casual affair, unrelated to other contemporary inventions and unheralded by prior developments. The hot-air balloon could have been invented at any time since the mastery of thin textile manufacture, which can be dated well before the Christian era. The hydrogen balloon could not have come about until after Cavendish had isolated the gas in 1766. As it finally turned out, both types of balloon were invented in the year 1783.

Although early meteorological records were naturally confined to the weather experienced at the surface of the Earth, as soon as meteorology began to be a science it was realized that what went on above the surface was important and that the physics of the air needed to be studied in three dimensions. An obvious illustration is the use made of cloud observations—the nature and structure of clouds, the method of their formation and their movement. Something could be learnt on those questions by observations from the ground, aided by such a simple instrument as the nephoscope. Most people, and certainly all concerned with navigation, know that the movement of clouds may be very different from the wind at the surface. It was also realized that since the atmosphere is a heat engine a knowledge of the temperature of the upper air was required. Anyone who has climbed a mountain knows that the temperature falls, and this was confirmed for the free atmosphere by observations with kites. It was clearly of interest to know whether the fall of temperature was maintained until the absolute zero was reached, and if not, why not. It is in the measurement of temperature and wind in the upper air that balloons have found their chief use.

For a number of purposes it is convenient to have a platform floating at a constant level high up in the atmosphere. This can be contrived by the use of a special arrangement of balloons for heights up to about 100,000 ft. There are at least three ways in which this can be achieved. In the first an extensible balloon is filled with sufficient gas to give it buoyancy for a definite rate of ascent. As it ascends and the atmospheric density decreases, the gas and the balloon expand and if the ascent goes on long enough the balloon bursts. If when the balloon reaches a certain dimension (or alternatively when the exterior pressure falls to a certain figure), a valve opens and allows sufficient gas to escape to stop the ascent, the balloon will float in equilibrium. A second method is to use a non-extensible balloon only partially filled with gas and with an open mouth; as the balloon ascends, the gas expands to fill the whole balloon and overspills thereby reducing the rate of ascent until equilibrium is reached. A third method involves the use of a number of extensible balloons tied together. When they have risen in the air and the balloons have stretched, some will burst before others and thereby a rough equilibrium is attained and the remaining balloons will float at nearly a constant level. A variant of this is to detach some of the balloons from the assembly at a predetermined pressure level, so that the remainder are just able to support the instruments and equipment.

We have followed what has been written in this Journal about the accuracy of dead reckoning in the air and the determination and use of the most probable position. We wish to refer in particular to the article by J. B. Parker entitled ‘The navigational implications of Mr. Durst's paper’ (this Journal, 8, 113). We are not familiar with the routes of the North Atlantic or Central Africa; we have, however, eight years experience on the routes Lisbon–Luanda–Lourenço Marques, via Dakar, as well as those overflying the Sahara Desert via Oujda and via Agadir. The following considerations are in great part the result of that experience.

In his Presidential Address, Captain A. M. A. Majendie emphasizes the value of the Institute in preserving the essential link between theory and practice. Particularly in aviation there is a risk that the ingenuity of the designer will lose value unless it is directly associated with the practical work of the operator. As airborne equipment becomes more complex, the operator cannot hope to grasp more than the fundamentals of much of the theory behind it, and his criticisms must perforce be tentative and somewhat uncertain.

In Dr. Derek Price's most interesting article ‘Two Mariner's Astrolabes’ he suggests that the heyday of this instrument was from 1530 to 1630. Some additional light is thrown on the closing date of the period of use of the astrolabe by Seller's Practical Navigation, a book which ran into many editions, the earlier ones being now somewhat rare. Successive editions of a book are usually of little value in giving a terminal date for the era of an instrument, for descriptions of it are only too often left in, unweeded long after the instrument is obsolete. Here, however, we have a description of the astrolabe inserted in the first edition of 1669 while it is omitted from the second edition of 1672. This later edition shows signs of careful rewriting and the fact that the author has expunged mention of some instruments, while retaining descriptions of others which never had much vogue, would seem to indicate that he thought that those which he had deleted would no longer be of value to the seaman.