In recent years, the most striking development in the philosophy of navigation has surely been the change in attitude towards errors. Ten years ago an error was regarded as something that just did not happen in the best navigational circles; today we accept it as the normal concomitant of observation, and we study to reduce it.

This change in philosophy is really nothing more than theory following in the footsteps of the practical man, for the practical man has always regarded a position plotted on a chart with a certain amount of healthy scepticism. It may therefore be of value to discuss the whole business of errors from the point of view of the practical man, avoiding complicated mathematics and dealing in demonstrations rather than in rigid proofs. Navigation has been described as the business of conducting a ship on its way across the sea or an aircraft on its way across the sky. The word conducting implies safety. Indeed, safety is the keyword in navigation.

In 1877 a two-volume book, Nouvelle Navigation Astronomique, edited by the astronomer Villarceau and a naval officer, Magnac, was published in Paris. The book, which may be considered the most comprehensive work on astronomical position lines up to date, covers completely the theoretical treatment of circles of equal altitude on Mercator projections and their practical evaluation, and considers the effects of possible mistakes and errors. In the present writer's view these factors have not yet been sufficiently appreciated. It is surprising that similarly detailed descriptions of the other position lines used for navigation have not yet been published; although, apparently, the attitude towards these questions has altered since that time. The change in methods of navigation, particularly with the introduction of radio aids, has brought a variety of other position lines to the fore, and the predominance of Mercator's projection is not as universal as it was eighty years ago. In order that these premises may be clarified, a summary of the various position lines in use today is here given.

This paper discusses celestial navigation within the Arctic Circle by the use of great-circle position lines. Application of this method in this area is indicated by:

(1) The freedom from need to correct for atmospheric refraction.

(2) The lack of dependence on either D.R. or assumed position.

(3) The simplicity of drawing the great-circle position line.

(4) The freedom from need for making instrumental scale readings and corrections thereto, other than in respect to the time of the observation.

The adequacy of available stars is examined.

A member, Mr. R. G. Bolton, has sent us the following graphic account of refraction, observed from Littlehampton jetty. The ship is a small coaster observed between 1 and 2 p.m. on a hot and sultry summer's day.

Timed sextant observations of the Moon when it is suitably limbed are obviously as easy to take as those of any other body, and the results obtained are no less accurate or reliable. It is therefore surprising that only about 5 per cent of Merchant Navy navigators appear to take sights of the Moon, and that about 75 per cent of the defaulters seriously believe the Moon to be of small value for navigation, other than for compass checks.

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.

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.

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.

The 600-ton Norwegian sealer Norsel, commanded by Captain Guttorm Jakobsen, made the last of her annual relief trips to Queen Maud Land when she went south last December to bring home the Norwegian-British-Swedish Antarctic Expedition from Maudheim. During this trip the writer was attached to the expedition as naval observer. The ship remained at Maudheim for three weeks while an aerial survey was being carried out by the Swedish air unit which she had brought with her; during this time advantage was taken of fine weather and favourable ice conditions to make two survey trips along the barrier, one to the eastward and the other to westward from Norsel Bay where the ship was harboured.