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 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 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?’

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.

Consol is the name now given to a navigational aid developed by the Germans during the war. A Consol beacon broadcasts on a medium frequency a pattern of dots and dashes, and by listening to this pattern on an ordinary ship or aircraft wireless receiver a navigator can determine his bearing from the beacon with a much greater accuracy than is possible with a D/F loop. The accuracy of the bearings obtained depends on the bearing of the observer from the beacon; it is greatest along a line called the normal of the beacon and decreases until it is zero along a line at right angles to the normal. The useful coverage with the existing type of beacon is about 280° out of 360°. With such a beacon the range over the North Atlantic is about 1200 n.m. by day and 1700 n.m. by night; the probable error on the normal is by day about ⅙° and by night (at ranges greater than 500 n.m.) about ½°.

Pressure pattern flying embraces a number of air navigation techniques all of which have one common feature: they relate pressure distribution along an aircraft's flight path to that component of the wind which acts at right angles to the aircraft's heading. My intention is to give a brief outline of the theory underlying these techniques.

Wind is brought about by horizontal pressure differences in the earth's atmosphere. Air tends to move from an area of high pressure towards an area of low pressure under the influence of the pressure gradient force. The direction of its motion is, however, affected by the earth's rotation in space. Considering this rotation in the horizontal plane only, it is at a maximum at the poles and zero at a point on the equator. At any intermediate point of latitude ϕ, the speed of rotation in the horizontal plane is proportional to the sine of the latitude. In the northern hemisphere the rotation is anticlockwise; in the southern hemisphere it is clockwise with reference to outer space.

The navigational problem. In order to find out how an aircraft is tracking with respect to the ground, we can either obtain information from data accurately placed with respect to the ground, or assess the horizontal movement of the air masses through which the aircraft is flying and combine this motion with that of the aircraft through the air. To determine the track we require accurate knowledge of the aircraft's heading and of the drift, which is the effect of the beam component of the wind. Along any given course line the navigator can make a series of drift observations, usually visual and therefore requiring downward visibility, and estimate the departure from the course line by averaging such observations to obtain the integrated effect of the drift. Since the sole purpose of drift observation is to estimate the departure of an aircraft from a given course line, a method of obtaining this total departure from a single observation or pair of observations, under any visibility conditions, is of considerable value. Again, if it is possible to estimate before flight the total integrated effect of drift for the whole flight, and our object is merely to fly to reach our destination, then the necessity of taking drifts during flight will be obviated.

The preceding papers indicate that the theory of pressure pattern flying assumes that the wind satisfies the conditions imposed by the geostrophic wind equation and that the atmospheric pressure distribution is not changing. These conditions are not satisfied in the atmosphere, and the errors caused by their non-fulfilment are discussed in the following paragraphs.

Effect of departures of wind from geostrophic. The geostrophic wind equation is derived on the assumption that the wind blows uniformly without acceleration and without friction. These conditions are never satisfied in the atmosphere, nevertheless the practising meteorologist has found that the geostrophic wind represents a useful approximation to the true wind. There are certain exceptions of which the most important are in low latitudes and at levels below 2000 feet.

Since the inauguration of the B.O.A.C. Return Ferry Service, the principles of pressure pattern flying have been followed on the North Atlantic as regards flight planning. In co-operation with the forecaster the practice developed of working out a number of flight plans to achieve the shortest possible flight time, and eventually it became possible to select the most favourable route with a reasonable degree of precision.

The advent of the radar altimeter furthered development of the pressure position line theory which I believe was first propounded by R.A.E., Farnborough, and has since been elaborately garnished and enthusiastically tested by our American friends during recent years. The words ‘altimetry’ and ‘aerologation’ have been added to our generally common language to cover flight techniques that might perhaps be more simply described as ‘pressure comparison navigation.’

Why the perfect air map does not exist. Air maps have been struggling for years to reach perfection; most of them fall far short of it for three main reasons:

(1) Maps are designed by highly skilled specialists who, however, do not generally know from first hand experience what the practical requirements are. They rely on hearing of these from practical airmen.

(2) The better the practical men are at map reading the less able they are to put into words how they set about it and what is required for the ideal air map.

(3) Map production is extremely expensive in time, work and materials with the result that map makers are loath to scrap a map once made, if it will ‘do,’ even though they realise it might be improved.

At the first International Meeting on Radio-Aids to Marine Navigation held in London in May 1946 some 105 delegates of twenty-three maritime nations met to discuss and witness demonstrations of some of the remarkable advances made in radio-navigation during the war and to consider the progress made in relation to their peacetime uses for marine transport.

At the invitation of the U.S. government a second meeting was held a year later, in New York and New London, to show the progress made in America, to illustrate, with demonstrations, the U.S. policy and to pave the way to international standardisation. The U.K. delegation was led by Sir Robert Watson-Watt.

The mariner has for many years been able to procure charts for practically any waterway in the world and in most cases has the selection of a variety of scales to suit his purposes. The air navigator has not been so happily placed.

Shortly after the end of the 1914–18 war the nations subscribing to the International Convention to Air Navigation agreed the need for world cover in aeronautical charts at various scales, but, up to the commencement of the last war, the 1:10,000,000 basic map, for which the French government accepted responsibility, was the only series to reach completion. Various areas were also charted at scales of. 1:1,000,000 and larger.

Following extensive demonstrations of radio-aids to navigation, telecommunication equipments and associated electronic developments, in U.K. from 9 to 26 September, in U.S.A. from 7 to 26 October and in Canada from 28 to 29 October 1946, the first session of a Special Radio Technical Division of PIGAO was held in Montreal from 30 October to 23 November 1946. The final report of this first session has been published as an ICAO Document, No. 2553/COT/26, and the portions dealing with radio-aids to navigation will be of interest to members of the Institute. The report cannot be regarded as ‘a formal ICAO action’ since it has not been adopted by the Interim Council, and from the U.K. point of view there have been a number of reservations in matters of detail.

There was, during the recent world war, and is still, an urgent A need to provide coverage over meteorological conditions in the North Atlantic, with particular reference to temperate and high latitudes, where changes are rapid and non-seasonal. In addition, and of great importance to the security of trans-ocean flying, is the need to provide intermediate points on the air routes for air-sea-rescue duties and to act, if required, as communication links. If ships can be permanently stationed at specially selected points they can form valuable additions to the W/T direction-finding network, and more accurate fixes will be obtained of any distress signals which may be sent out by aircraft.

British south american airways have recently been carrying out a series of tests on flight refuelling. The first of these tests took place over southern England and were carried out on a scheduled basis at various heights both by day and by night and all proved successful—with the exception of two which were cancelled on account of bad weather, that is, bad weather on the ground and not in the air. The second part of the series has now taken place and consisted of London-Bermuda-London return nights on a weekly basis for a period of three months.

The process of flight refuelling does not in fact involve any particular navigational problem, but rather the simple problem of ‘approach’. The aircraft admittedly must intercept, but thanks to the fact that various devices are used for the actual approach of one aircraft to the other the navigational accuracy required for the interception is not at the moment of a very high order.

At 2215 hours GMT on 21 September 1947 the U.S.A.A.F. All-Weather Flying Centre's Automatic C54 took off automatically from Stephenville, Newfoundland, and twelve hours and five minutes later landed at Brize Norton, England. Neither pilot nor navigator had interfered with the automatic equipment during the entire flight. What, briefly, is the navigation equipment and procedure employed on such a flight?

Equipment. The navigation equipment consists of three magnetic heading selectors, two air log units or AMUS and a radio compass which will automatically switch to a number of preselected frequencies.