This paper describes a method for the reduction of simultaneous star altitude observations in pairs, whereby an unambiguous ‘fix’ is obtained without reference to the dead reckoning position and without use of the intercept procedure. The method is adequate in all latitudes. An especially swift reduction is possible for the moments at which two stars are situated at equal altitudes.

When position is determined by means of two simultaneous star altitude observations and use is made of a single chosen position it is possible for the Marcq St. Hilaire intercepts to be so short that they can be regarded as negligible. When this occurs the chosen position is, in effect, the true position as indicated by the observations and no further work is required for a fix. If, in such a case, it is desired to have the Sumner lines of position represented on the chart it will be possible to draw them through the chosen position. The selection of such a chosen position may be made with certainty, in every instance, by computing numerical values for the latitude and the longitude of the appropriate intersection of the two circles of equal altitudes corresponding to the corrected observations. If the entire computation had to be done after the observations were made, the labour of this procedure would prohibit its use in rapid navigation. It happens, however, that the greater part of the work can be precomputed and presented for the navigator's use in a tabular form. These data are extremely compact and are permanent except for the need of occasional adjustment for precessional effects and on account of proper motions of the stars. No almanac would be required for use with such a table if the navigator were not dependent on it for his G.H.A. Aries. No knowledge of the dead reckoning position is employed in this computation; star observations suffice to determine the position without ambiguity.

The four papers which follow were read to a meeting of the Institute held at the Royal Geographical Society on 19 May. They provide an account of the four systems of radio position fixing that are most widely used at sea, and give both a description of the experience gained and a general survey of what has been achieved since the international meetings on radio aids to marine navigation were held in 1946 and 1947. Certain requirements for marine radio position fixing systems were formulated at these meetings and a measure of agreement was reached on the types of navigational aid which should be developed. This review of the four principal systems, and of aspects of some of them which may not be widely appreciated, may perhaps give an opportunity for assessing how much progress has been made over the last few years and of the problems that remain to be solved.

The four papers printed here were read to a meeting of the Institute held at the Royal Geographical Society on 17 February 1950. They present, each from a detailed experience of particular requirements, an enquiry into one of the major problems of flight operation at the moment. It is clear, both from the papers and from the nature of the problem itself, that no solution can be considered apart from its navigational aspects, and that the whole conception of control is inevitably bound up with the question of position. The problem is therefore of its essence a navigational one.

The Institute has now completed two years of its existence. The papers which have been read before it during these two years have covered a wide range of subjects and have served to emphasize the many ramifications of the science of navigation. Because of the high speed of modern aircraft, air navigation presents more problems and of greater variety than surface navigation, but even on the problems of surface navigation there has been ample scope for a wide range of discussion. The Institute has taken a prominent part in the discussion of the proposals for the revision of the Abridged Nautical Almanac. It might with some reason have been supposed that there was nothing more to be said on the methods of reducing astro-sights and determining position at sea. The problem is perfectly straightforward and there is a limit to the number of different ways in which the spherical triangle can be solved. But the essential basic data can be presented in a variety of ways, while there are many possible methods of presenting tables for the solution of the spherical triangle. The decision to use Greenwich hour angle instead of right ascension in the Abridged Nautical Almanac has followed its adoption in the Air Almanac; the revised Almanac will have an entirely different format from the present, while the methods of reducing sights must be correspondingly modified.

Before the war the only radio navigational aids in current use by shipping were direction finding systems, operating in the medium frequency band of the radio spectrum.

During the war, not only were many new types of position fixing systems evolved, but radar techniques were also developed, thus making available a wide range of new facilities of potential use both to ships of many different categories and to port and harbour authorities for the supervision of marine traffic.

The effect of radar on the application of the Rule of the Road at Sea has been given attention in several papers and discussions in recent months. Deductions on their relationship have been attempted, and already judgements have been delivered in the courts of this and other countries which take account of the installation of radar in one or both of the parties to a collision. The suggestion has been seen that guidance to mariners concerning their actions and responsibilities when radar is fitted must await the development of case law. This development will be a lengthy and probably painful process and the object of this paper is to discuss the possibility of establishing principles which would enable the great potential value and legitimate application of radar to be established without waiting for casualties.

In his Presidential Address to the Institute this year the Astronomer Royal, Sir Harold Spencer Jones, stresses the importance of an early resumption of the general survey of the Earth's magnetic field and developments in airborne magnetometers in the United States have suggested the possibility of using aircraft for this purpose. The techniques which are available for aerial survey will be discussed in this paper and an attempt will be made to evaluate the relative merits of conducting world wide magnetic surveys by sea and by air.

There has always been, since the very early days of aviation, some form of control exercised over air traffic, an attempt to curtail random activities. The earliest example is perhaps that of the somewhat unfortunate individual who was obliged to stand for long periods in a highly dangerous position at the end of a paraffin flare path. This example shows how soon it was realized that where a collection of individual units are all trying to get to the same place, some of them possibly at the same time, some co-ordination and orderliness must be introduced, and that this could only be achieved by some third party. It was soon seen that certain difficulties prohibited individual countries from making their own decisions on these matters and that, like the high seas, aviation requires a common ‘highway code’. With the ending of the first world war, and the beginnings of international aviation, came the formation of the International Commission for Air Navigation, which had amongst its objects the agreement between contracting states on standardization of rules of the air, and of visual and aural signals. It might well be said that, out of I.C.A.N., air traffic control was born in the period 1919–20.

Before considering in any detail the importance of precise navigation to air traffic control, or attempting to define the word ‘precise’ in this context, it seems desirable to go back to fundamentals and consider certain essential characteristics of a volume of traffic flowing between individual pairs of airports in a system comprising a large number of such airports, randomly distributed and heavily loaded.

This paper is concerned primarily with an investigation of the loxodromic distance between two points on the spheroid. This is derived by a modification of the meridional parts method in terms of the track angle and the difference of latitude reduced by a correction which is a function of the latitudes concerned.

Since the method is unsuitable when the track angle is near to 90°, the known formula for the mid-latitude correction is examined and an alternative method suggested for use in this case.

The results obtained are compared in a practical example with those found by the usual methods, and finally means are proposed by which the refinement described above can be incorporated into current plotting practice on aeronautical Mercator charts.

Practical experience in radar-assisted marine navigation has shown that the closer one is to the general land areas, navigational seamarks, &c, the easier position fixing from radar information becomes, although some particularly congested and confined waters provide exceptions to this rule. There are usually large numbers of more suitable targets available at the closer ranges, and increased ease of identification results from objects being closer to the observer. The latter effect, of course, arises from initially knowing one's position more accurately, and this in turn is based on the shorter ranges at which bearings and/or ranges are being taken.

Direction finding is the oldest, simplest, and probably most reliable radio aid yet offered to the mariner. In some ways it may be likened to a magnetic compass and, if its range is very much smaller, it has the inestimable advantage over a compass of giving bearings on a very large number of stations instead of one only. It is the only navigational aid, other than radar, in which the performance is controlled by the shipborne installation and is not subject to technical failures which may occur on land-based transmitters.

An abbreviated version of a paper read before a joint meeting of the Institute and the Royal Aeronautical Society.

The usefulness of a particular aircraft may well depend upon the availability or simultaneous development of equipment. Safe, reliable, economic and speedy operation in the civil field may rest, for instance, on facilities which enable all-weather operation to be undertaken—including navigation, traffic control, approach and landing facilities. Military operations, even more directly, will be determined by the instrument aids available.

This paper deals with the improvement to be gained by using position lines from two Decca chains to obtain a fix in areas where a single chain fix is liable to extensive errors.

Recently The Decca Navigator Company, with the cooperation of the Admiralty, undertook a series of trials between Scotland and southern Norway, using the English and Danish chains of stations outside the normally used coverage of either chain. The results obtained were highly satisfactory and an account of them is given in this paper.

The high concentration of aircraft near aerodromes, with consequent collision risk is well known. It is at present necessary, in poor visibility, to guarantee the indispensable commodity of safety by the sacrifice of schedule regularity and fuel economy. So long as this is the case, the problem of terminal navigation and control must be regarded as one still demanding a satisfactory solution.

The determination of a ship's position by means of radio observations from fixed shore transmitters has now been practised for a considerable period of time, but up to the outbreak of the last war the accuracy obtained from the conventional direction finding systems then in use was only sufficient to provide a general estimate of position suitable for off-shore navigation in waters where the ship's position need be known only to within a mile or two. It was not until, under the pressure of wartime requirements, the modern range of radio aids to marine navigation were produced that means were provided by which the mariner was enabled to determine his position with an accuracy comparable with that of the best visual fixing but with the great advantage that these observations could be made in all conditions of visibility and weather. At the end of the last war there were three systems of outstanding merit available: Gee, Loran and Decca. All three systems, as is well known, employ a combination of master and slave stations, the transmissions of which provide radio position lines capable of accurate calculation and plotting on navigational charts.

In daylight and in good visibility no mandatory flying control is either necessary or desirable. The basic task of air traffic control is therefore (a) to give information so as to expedite landings and take-offs in good flying conditions and (b) to give information and instructions in blind flying conditions or at night.

As between the scholar and the technician, the armchair theorist and the practical man, the antagonism is as old as civilization itself. In Queen Elizabeth's days the gentleman born was the only gentleman, however ignorant, while learning was the preserve of the universities; the practical man was a mere ‘mechanician’. But there was some liberal thinking, common-sense thinking, even in those days, and one Gabriel Harvey, a well-known literary man and controversialist, spoke up boldly for the technicians. Even though they had heard no university lectures, he said, and were deficient in book-learning, it would be a bold man who would despise such expert practitioners as Humfrey Cole, the mathematical instrument maker, William Bourne, the naval gunner, Matthew Baker, the shipwright, John Shute, the architect, John Hester, the chemist, and Robert Norman, the hydrographer and compass maker. No fewer than four out of the six notable men he named were doing work that was relevant to the advancement of the navy and navigation. They were at the height of their powers in the decade preceding the defeat of the Spanish Armada, a coincidence which cannot be without significance.

The present-day trawler carries more aids than any other vessel of comparable length and tonnage and, more often than not, more than the majority of big liners and cargo ships. She carries a powerful wireless transmitter giving an output in the neighbourhood of 100 watts in the modern sets; a main receiver with a standby, or emergency one, for listening in to ships of the same Company for information regarding the state of fishing in their areas; and one or two direction finders, one of which (known as a ‘fish snatcher’) is tuned to the trawler wave band to take snap bearings of rival ships who may be on a better living and foolish enough to say so. So far as Consol is concerned the direction finder is used to ascertain the sector in which the vessel is, should the accuracy of the dead reckoning position be in doubt.