The aim of the Duke of Edinburgh's Lectures is ‘to extend the horizons of navigational interest’. I have been able to interpret this literally, for if you extend these horizons far enough, what do you arrive at but the subject of this lecture, the shape of the Earth? It is a subject which has been revolutionized in the past five years by analysis of the orbits of artificial satellites: the two years from 1958 to 1960 saw more progress than the previous 200 years, and since 1960 the pace of progress has shown no sign of slackening.

Through the interest of Mr. S. M. Burton, I have recently seen for the first time the comprehensive proposals for ‘astrofix tables’, compiled by Gilbert F. Cunningham, B.A., Ph.D. (then Staff Navigator, R.A.F.V.R.) and submitted to the Empire Air Navigation School at Shawbury in May 1945. Dr. Cunningham, a member of the Institute since 1948, is no longer actively engaged in the field of navigation, and he has therefore agreed to allow me to describe in the Journal those features of these proposals that are both new and interesting

The following discussion took place at a Technical Session of the Institute held in London on 24 May 1963, with the Chairman of the Technical Committee, Wing Commander E. W. Anderson in the Chair. Opening the discussion, the CHAIRMAN suggested that the problem might first be examined from the point of view of (a) a tactical solution and (b) a strategic solution.

For some time there has been an interest in nautical circles in the effect of temperature-differences between air and sea on the dip of the horizon. In about 1900, from his observations on board K.K.S. Pola, Koss established a relationship between the dip and the temperature-difference between air and sea, and an attempt was made, without much success, to produce corrections based on this relationship. New observations seemed only to add new uncertainties. A recent comprehensive review of the subject draws the conclusion that for practical purposes it is impossible to calculate the dip from measured temperatures by means of theoretical or empirical formulas. Indeed it is not possible to calculate the dip from simple measurements of temperatures at a given point to within o′·1 or o′·2. Horizontal irregularities, especially of thermal stratification and of wave height, always cause deviations of the dip from its calculated value. Nevertheless it is sound practice to correct the mean dip for temperature differences between air and sea. An analysis of observations where there are large temperature-differences—i.e. cases where the correction becomes noticeable—shows that the dip is greater or smaller than normal if the air is, respectively, cooler or warmer than the water. Out of 179 observations made by the Institute of Geophysics at Hamburg University with temperature-differences between air and sea greater than 2°C, not a single observation did not obey this rule.

This paper first considers the characteristics of the supersonic transport aircraft (S.S.T.) as established by various international authorities and, on the basis of these characteristics, endeavours to deduce the operational requirements for a navigation system. An indication is then given of the extent to which low frequency radio aids (such as Decca and Harco) can meet these requirements in the subsonic, transition and supersonic flight regimes, whilst discussing the relationship of these ground-based systems to self-contained aids. The paper was presented, in a fuller version, at the meeting of the Deutsche Gesselschaft fiir Ortung und Navigation held in Berlin, 22–7 April 1963.

When radar is used at sea as an aid to collision avoidance, the necessary information has to be obtained by maintaining a plot, which, however, can only offer the average course and speed over a passed time. It is not a reliable prediction of future actions, so that to make too long an extrapolation from a plot is hazardous. It might in some circumstances be better if a ship could be called up by radio and asked her intentions, though this requires first a knowledge of her identity and call sign.

This paper outlines a system of communication that would make it possible to call a ship (fitted with the necessary receiving equipment) initially located only by range and bearing, to obtain the identity of the ship and establish courses, speed and intended actions, and if necessary, radio call signs and calling frequencies. The messages passed by a ship would be recorded automatically. It is proposed that the system should have an operating range of 15 miles, though this does not represent a limit to the range possible. There are objections perhaps to trying to get out of a mutilateral situation of danger by bilateral agreements, and at least one school of thought would hold that the danger is likely to be increased by relying on communication. Nevertheless the system described here holds considerable interest and might, as the author suggests, serve other purposes at sea.

The method of finding the latitude of a ship at sea from an observation of the Sun or other body near the meridian is practised extensively in the Merchant Navy. The history of the method, which dates from the middle of the eighteenth century, is full of interest: and the ex-meridian problem is almost as celebrated in the history of nautical astronomy as the double altitude problem. Considerable attention was devoted to the ex-meridian problem during the last century—a period which was, in truth, the golden age of astronomical navigation. Many ingenious solutions were contrived and a diversity of ex-meridian tables were constructed, all aimed at facilitating the problem of finding latitude at sea.

Among many records of the first circumnavigation of the globe preserved in Spain is the log-book kept by the pilot who brought the Victoria home—under the command of Sebastian de Elcano. This pilot's name was Francisco Albo. He signed on in the first instance as master's mate of the Trinidad, Magellan's own ship, which did not return. Although a native of the island of Rhodes, he was thoroughly grounded in the Portuguese method of navigation—by observation of the noon Sun. It involved the use of a four-year table of declinations, and an English version of this very table and instructions was presented to Henry VIII about 1540 by Roger Barlow, who was urging an English participation in the new discoveries.

Very shortly after the second world war merchant seamen found that they had inherited a device which shipbuilders and owners fondly imagined would prove to be an infallible safeguard against navigational hazards: this was radar. After fifteen years had been devoted to examining the disappointing results provided by the new panacea, the International Conference on Safety of Life at Sea, held in London in i960, finally published a radar code. So eagerly had this code been awaited that the Conference recommended its issue without waiting for the new international convention to be implemented.

The Sun-Star Chronometer described in this note has been developed by Raymond Nardin of Switzerland and Oscar E. Batori of the United States; it is manufactured by Ulysse Nardin and produced by the Batori Computer Company Inc. of New York. It contains interesting features which merit description.