The statistical relation between wind and temperature in the lower stratosphere is not only of theoretical interest but is of practical concern for the operation of supersonic aircraft since for example the incidence of abnormally high temperature together with strong head-winds could substantially increase the time of flight and reduce the pay-load. Temperature and tail-wind component have been correlated on the great-circle route between London and New York at 50 mb. The route was divided into six legs of approximately 500 nautical miles; at the mid-point of each leg, temperature and tail-wind component for an eastbound flight were obtained from daily charts for the period of the International Geophysical Year and its extension, July 1957 to June 1959 (U.S. Weather Bureau, 1960–63). Seasonal correlation coefficients were evaluated for each leg and for the route as a whole. The seasons in the lower stratosphere in middle latitudes differ from the conventional seasons except in summer (June–August). Although autumn has been taken as September–November, it appears that the transition to the winter type of circulation is usually completed by late October so that November should strictly be included in winter. However, the period December to March has been taken for winter; conditions in March are very variable from one year to another but on balance this month is probably more appropriate to winter than to spring.

Traditionally ‘Freedom of the Seas’ has meant that the ‘Master under God’ has been answerable to no one for his ship handling and manœuvring, except in the case of collision, when he has been answerable to the Courts. Congestion of certain sea areas and waterways has created situations where some restriction to this freedom has become acceptable in the interests of general safety; harbour radar procedures, the Dover Strait and other traffic separation schemes are the most well-known examples. Such areas will increase in number and size as the volume of trade increases.

An accuracy contour can be defined either in terms of a locus of constant radial error or a locus of constant probability density. A short comparison of the two concepts is given in reference 3.

The object of this note is to define contours of constant probability density in the case of a two-position-line running fix; the outcome is of interest in that it enables the navigator to plan his observations so that the accuracy is optimized. In Fig. 1 the object observed is S. The transferred position line corresponding to the first observation is drawn from the point S′, where SS′ is the vector corresponding to the ship's run during the time between the two observations. The fix is at O.

In January 1967 the Centre National d'Etudes Spatiales and the Secrétariat Général à l'Aviation Civile agreed on the definition of the main characteristics of the Project Dioscures, a system for telecommunications, air traffic control and navigation by means of satellites. Since then, technical studies have been carried out and the main equipment is being developed. The proposed system will enable air traffic control centres to provide continuous position determination for aircraft in the common visibility zone of two geostationary satellites. Furthermore, it will establish dependable and good-quality communication links between aircraft, control centres and other users (airlines and shipping companies, meteorological services, &c.). The system will initially be implemented over the Atlantic, mainly to serve the North Atlantic region, to be progressively expanded to cover the whole world.

The definition of the word ‘navigation’ has been discussed frequently in meetings of this Institute and a very flexible thing it appears to be, varying its scope to suit the lecturer. This is not really surprising however, since whatever we think of as ‘navigation’ is only part of the wider business of living. In aviation for instance, the business of ‘conducting a craft as it moves about its ways’ can legitimately include seeing that the fuel tanks are full as well as pulling back on the stick to avoid hitting the top of the hill.

Using a Kelvin-Hughes radar photoplot an investigation of sea-clutter patterns on the radar screen was carried out during two voyages in the Atlantic during 1964 and 1965. A physical explanation of sea clutter has not yet been produced. The Use of Radar at Sea states (page 101): ‘In almost all sea conditions there will be an area of sea clutter around the ship. The fronts of waves give stronger echoes than the backs and therefore the clutter area will not be symmetrical about the ship.… If the movement of the sea is largely due to swell there will be a wider space between echoes although they will extend to some distance. Lines of rollers sometimes produce very distinct echoes.’

To help him in his use of radar as an aid to avoiding collision in fog, the watch officer needs to be sure which targets appearing on the radar screen are potential hazards, including those with which the collision risk will be increased by alteration of his own course and/or speed made to avoid other ships or in the course of navigation. In the commonly encountered multi-ship situation there are therefore likely to be at any particular instant several ships, perhaps 10 or more constantly changing, concerning which detailed and up-to-date information is highly desirable. This detailed information is of two kinds, namely information concerning the motions of other ships relative to own ship, and information concerning the true motions of other ships.

The following analysis of collisions in the Dover Strait has been made by J. H. Beattie for the International Committee on the Organization of Traffic at Sea (Icotas).

A previous paper, developing the idea of automated routing of vessels stated ‘the full scope of automated systems at sea is inconceivable in terms of compliance with the old (collision) Regulations. Only an entirely new code of manœuvre will give the dimensions and scope needed.’ Again, it was suggested that the Collisions Regulations would need to be completely re-thought and re-written in the light of present capabilities and possibilities. This paper, while not endeavouring completely to re-write the Collision Regulations, tries to outline the form the new Regulations should take without entering into too much detail, with particular relevance to the traffic separation schemes presently under consideration by Imco and leading to the future prospect of complete automation as envisaged in the article under reference.

It took three years to gain acceptance for the provision, in crowded waters, of two parallel channels for the main traffic, each reserved for streams travelling in opposite directions. It then took another four years to obtain the corresponding marking in the Dover Strait, which served as a testing ground for the system. However, since this came into operation in 1967, there has been an amazingly rapid expansion of the organization of crowded waters. At a time when new schemes are being brought to the attention of seamen, it is important to take a close look at the authority which such regulations possess.

The navigator is frequently faced with the task of finding the course and distance along a rhumb-line between two places on the Earth's surface.

The following paragraphs tell of a two-part investigation into the methods of calculating rhumb-line courses and distances.

Part I deals with a comparison of the methods used and the results are presented in graphic form.

Part II considers the various corrections that may be applied to mean latitude sailing to get better results.

A Recent Admiralty Notice to Mariners (No. 1555/1968) advises that a vessel trading the southern North Sea and the English Channel has been fitted with experimental direction indication lights in order to indicate to an approaching vessel the direction in which she is altering course and the duration of the alteration. The positioning of these lights are 10·5 ft. higher than the after masthead light and 4 ft. outboard on each side of the centre line, and they are coloured red to port and green to starboard. When altering course the appropriate light flashes until the vessel is steadied up on her new course.

Having followed national and international shipping periodicals of the past years, one can readily observe that a signalling device installed on a vessel giving early and permanent signalling of the ship's course and manœuvre is urgently needed. In this report I will attempt to give brief information on previously known ideas, analyse them, draw conclusions and make a new proposal.

In a pungent note published in the October 1966 Journal (Bad Language, Journal, 19, 523), Wing Commander E. W. Anderson drew attention to some of the confusion that had arisen through lack of a precise and accepted navigational terminology. He suggested that if a number of the more contentious terms were defined and accepted by the Institutes of Navigation, the use of ‘bad language’ might die out. It has now been agreed that the British Standards Institution should compile a navigational glossary and to set things going the Institute has formed, under Wing Commander Anderson, a sub-committee to try to sort out some of the terms over which ambiguity has arisen.

Mr. Bell and Professor Stratton have in the October Journal shed interesting light on the nature of inertial navigation as applied to navigation around a planet. It is a pity that Mr. Bell has repeated that in such inertial systems vehicle position and velocity are deduced from measurement of acceleration. This idea is certainly misleading so far as understanding error propagation in these systems is concerned, if not actually wrong.

The aim of this paper, which was presented to the last meeting of Icotas (London, 14 January), is to show how the manœuvres proposed by Calvert (Journal13, 127) and by Hollingdale (Journal14, 243) could be incorporated in the International Regulations for Preventing Collisions at Sea. Calvert's objective was, as Hollingdale points out, to establish a set of manœuvres whereby a collision situation may be converted into a ‘miss’ of specified magnitude.