Men have always been curious to know the shape and size of the planet upon which they live. Most people have heard of the experiment by which Eratosthenes determined the circumference of the Earth, and the principle of his method underlies all subsequent determinations. What he did amounted to finding the difference of astronomical latitude between two places and measuring their distance apart in terms of a standard length (Fig. I). Astronomical latitude may be denned here as the complement of the angle between the vertical at the point in question and the direction of the Earth's axis.

There is rich material for studying navigation technique in the fifteenth and early sixteenth centuries in the volume A Marinharia dos Descobrimentos by the late Fontoura da Costa, which deals in great detail with the evidence for early sailing methods; the facsimile reprints of rare documents bearing on early Portuguese navigation lately published by Joaquim Bensaude for the Portuguese Government also contain much information on this period. The object of this article is two-fold: to establish that in an Addendum to one of these documents, the Reportorio dos Tempos of Valentim Fernandez (1st edition 1518), we have extracts from an archaic type of navigating manual; and hence to argue that, judging from his own words, Columbus (whose skill in navigation is a matter of controversy) had studied rules and instructions for navigation just such as the Addendum contains, but that owing to his lack of elementary mathematical training he had only imperfectly understood them.

On page 268 of Volume I of this Journal, published in July 1948, A. H. Jessell called attention to a simple method of correcting fixes, or position lines, deduced from astronomical data referred to a fixed epoch, for the effect of precession and nutation since that epoch. This paper has generally been regarded as the first reference to this method, but it now appears that (as so often happens!) it was anticipated by Lieut.-Commander M. Bini, Italian Navy, in ‘Principi di un nuovo metodo per la determinazione immediata del punto nave astronomico’ (On the principle of a new method for the immediate determination of astronomical fixes), a paper presented at the meeting of the Italian Academy of Sciences on 8 November 1947 and later published in Atti della Academia Nazionale dei Lincei (Series VIII, Vol. III, Nov. 1947).

An article by Bini, in which the possibilities of the method were touched upon, was also published in March 1947 in Rivista Marittima.

This paper describes two methods of determining whether a sextant observation of the Moon should be of the upper or lower limb. The first method requires the use of a celestial globe or planisphere; the second is mathematical and requires a certain amount of computation, but is exact.

The line which separates the dark portion of the Moon's disk from the illuminated portion is known as the terminator, and the straight line joining the ends of the terminator is that used in this problem. This line is always perpendicular to a line from the Moon to the Sun (the horns being always turned away from the Sun), so that its position can be predicted from the geometrical relations of the Earth, Sun and Moon. This enables the limb to observe to be determined.

The fact that the de Havilland Comet cruises at nearly double the flying speed and nearly double the flight altitude of comparable piston-engined airliners is a measure of the great leap forward in air transport which the introduction of gas-turbine engines has brought about. It also illustrates an inherent feature of jet aircraft, for only at high speed and high altitude do turbo-jet engines, and to a less critical extent turbo-prop engines, operate at their maximum efficiency, expressed in distance flown per gallon of fuel consumed. With reduction of altitude and speed, however, the fuel consumption does not fall off proportionately and efficiency decreases rapidly. For example, even when taxying on the ground the Comet's fuel consumption is about 70 per cent of that at cruising altitude, and when flying at sea level the still-air distance flown on a given quantity of fuel is less than half of that at cruising altitude. In other words you get the best out of a jet aircraft when you are going somewhere fast, and when the length of the flight is sufficient for the aircraft to climb to its optimum cruising altitude and remain there for a considerable proportion of the flight time.

Although the approximate position and strength of the main ocean currents have been known for upwards of two hundred years, it is only in the last few decades that oceanographers have attempted to explain them on the basis of sound physical theory. For many years the progress of oceanography was hampered by the lack of sufficient experimental data; today much new information is being gathered throughout the world, enabling existing theories to be examined critically and providing a basis for new work. It appears from the latest investigations that ocean currents are subject to quite large ‘synoptic’ changes superimposed on the general ‘climatic’ pattern in a similar manner to the movement of air masses in the atmosphere, but on a much reduced scale. This and other developments of theory during the century will be discussed in this paper.

The writer has compiled a table of altitudes and azimuths for the star Rigil Kent using as argument astrograph times, which are tabulated at four-minute intervals. The tables have been compiled for latitudes S. 35° to S. 39° but could, of course, be extended to all latitudes and for any star. In this note they will be referred to as the Astrograph-time Star Tables.

In December 1949 Adams and Uttley presented to a joint meeting of the Institute and the Royal Aeronautical Society a paper surveying the field of navigation systems for air use, in which they set out in some detail the principles, possibilities and limitations of the various aids which the scientist has to offer toward the solution of the navigation problem. In their conclusions they rightly pointed out that all these devices fall short of the ideal to a greater or lesser extent, so that the potential user is faced with the task of choosing from a bewildering and diverse array of imperfect systems those which are most likely to fulfil his needs.

It would be interesting and profitable to look back to see how closely the applications of science to the sea had followed its developments and technical achievements ashore. In contrast to the wealth of literature on the classical geography of the oceans and the achievements of the early voyagers there is no balanced account of the scientific investigation. Such an account would include the work of men like Boyle, who, in his observations and experiments about the saltness of the sea (1672), gave the first satisfactory explanation of this phenomenon, and showed th at it would be necessary to make a great number of observations in different climates and different parts of the world to determine the degrees of saltness with any certainty. He arranged for travellers to collect samples for him. Lavoisier (1772) and Bergman (1777) analysed samples of sea water and named the principal dissolved salts. In 1812, Alexander Marcet, a London physician, made the remarkable discovery that although the total amount of salt varied from place to place according to the balance of evaporation and precipitation, the principal constituents were always present in the same proportions. Although this was almost a premonition based on the analysis of not more than fourteen samples from different parts of the Atlantic Ocean, it has stood the test of time.

In 1947 it was felt by the Ministry of Transport that although the radar to be installed by the Mersey Docks and Harbour Board at Liverpool would demonstrate the suitability of this type of equipment in meeting the requirements of the larger ports, it was probably beyond the resources of many small ports and indeed was too elaborate for their needs. It was therefore decided that the Ministry's Operational Research Group should survey representative small ports in the United Kingdom in order to estimate the advantages that could be expected if shore radar were to be fitted and to discover what limitations there were likely to be in such fittings. As a sequel to this inquiry, it was proposed to select one port as the site for a trial, to be sponsored by the Ministry, in which a simple radar installation would be employed. The vital importance of having direct radio communication between ship and radar station was fully recognized from the start, and it was assumed throughout the investigation that this facility would be ancillary to the radar, the pilots probably carrying portable transmitter-receivers.

The Editor welcomes this opportunity of publishing an account of the valuable and fundamental work done by the Navigation Section of the Aeroplane and Armament Experimental Establishment at Boscombe Down. Some of the results have previously appeared in reports with limited circulation, but no full account has yet been published.

The Navigation Section of Aeroplane & Armament Experimental Establishment (A. & A.E.E.) had, at the outbreak of war in 1939, only recently been established, and was in the charge of Squadron Leader (later Air Commodore) D. J. Waghorn, who was followed by Wing Commander W. S. Jenkins. Both of these officers were keenly interested in methods of astronomical navigation, and in development work. Professor H. H. Plaskett, F.R.S., Savilian Professor of Astronomy at Oxford, was attached to the section, and brought to it an invaluable experience in observational theory and techniques.

The work of the section in the earlier part of the war mirrors exactly the state of knowledge in astronomical methods in navigation at that time. A bubble sextant, the Mk. VIII, had been in use for some time, although knowledge of astronomical methods was limited to comparatively few highly trained members of aircrew. The potentialities of astro-navigation were appreciated, however, and the Mk. IX sextant was being developed.

The purpose of an instrument let-down is to bring an aircraft past all hills and obstructions to a particular position at low height. If the pilot follows the correct procedure, the aircraft will obviously clear the hills and obstructions. But owing to various interruptions and distractions, difficulties of reception or the need to give partial attention to other duties, he is often unable to follow the procedure exactly; he will then want to know whether departure from the procedure requires immediate rectification, or whether he is at liberty to return gradually to the correct path. A badly working radio aid, or some other difficulty, may make it necessary to abandon a partly completed approach; he will then want to know the best way to extricate his aircraft from a possibly dangerous situation. Furthermore, the pilot often has to improvise an ‘intermediate procedure’, to connect between his arrival over the aerodrome and the beginning of the let-down. For these reasons he needs to know the positions of the hills and obstructions in relation to the let-down; and the only way to present this information to him quickly and unambiguously is by making hills and obstructions the principal features of let-down charts. The local knowledge possessed by pilots of scheduled services does not lessen the need for an effective presentation of this feature on the charts, as it is precisely when landing at unfamiliar aerodromes that the charts will be most used.

This paper was written in 1946 when Mr. Kiewiet de Jonge was a student at Harvard College Observatory. Subsequent developments in astronomical navigation, particularly the publication by the U.S. Hydrographic Office of H.O.249, have overshadowed the practical advantages of the three-star position tables. But the principles of the method, which have not previously been described in print, are of sufficient importance and novelty for permanent record.

In this paper we will develop a fast tabular solution of the position deduced from three ‘simultaneous’ sights. This is achieved in a novel way, through principles not generally associated with the traditional approach to the problem. The solution is based on the fact that the measured altitudes of a set of three stars uniquely define the most probable position of the observer projected on the celestial sphere.

The sixth International Hydrographic Conference, at which the Institute will be represented by an observer, is being held in Monaco at the end of April. It is therefore appropriate that we should at this moment publish an account of the work of the International Hydrographic Bureau, which has been written for the Journal by the President of the Bureau's directing committee.

The conservancy problems of any modern major terminal port are governed by certain features. In this paper the Port of Southampton is examined within the context of these features and certain significant facts are recorded; recent work to improve the facilities of the port is then described and possibilities of further long-term development are discussed. The features referred to may be classified as:

(i) The geological history.

(ii) The tidal regime. In particular the spring lunitidal interval and range, the times, direction and rate of maximum tidal streams and relation to local high water, duration of slack-water periods and particularly that phase of the tidal stream which is dominant in rate.

Amongst the schemes for simplifying the processes of astronomical position fixing the family of multi-star sextants contains some interesting material. By the simultaneous observation of two or more stars through an optical system coupled to a gravity reference, it is possible to determine the observer's position directly in latitude and longitude, with little or no computation.

The number of instruments on these lines which have been designed is very large and it would not be possible to describe them in detail in the course of a short paper. A few remarks about their principles may, however, be of interest since they are, in general, sound in theory and fall short of practical requirements only because, when used on an unstable platform such as a ship or aircraft, they make too heavy a demand on the skill of the observer.