The position of a point on the surface will then be expressed by two spherical coordinates: namely, ist, the distance of the point from the primitive circle measured on a secondary; 2nd, the distance intercepted on the primitive circle between this secondary and some given point of the primitive circle assumed as the origin of coordinates.—William Chauvenet, Manual of Spherical and Practical Astronomy (1896).

On 16 May 1870, exactly eighty years before this paper was written, Lord Kelvin, then Sir William Thomson, worked out an epoch-making example of how to find the hour angle and azimuth of a heavenly body by inspection, in order to facilitate the use of Captain Thomas Sumner's method at sea. His work was published one year later in the Proceedings of the Royal Society, and in it he describes a page of his new Tables for Facilitating Sumner's Method at Sea. These tables, comprising nine pages, were made public on 11 November 1875 and were published in London in May of the following year; from them have been derived all modern navigation tables based on right-angled spherical triangles. Kelvin then used, for the first time, Greenwich hour angle in arc and assumed latitudes and longitudes. (The writer has himself used G.H.A. in arc since 1902 and assumed positions since 1908.)

Recently an electromagnetic method for measuring the velocities of ocean currents for oceanographic purposes has been shown to be reliable enough for the observed velocity of the surface current to be taken into account in dead reckoning navigation in the open ocean. A preliminary test of the electromagnetic method as a navigational aid was made in 1949 on one cruise covering a distance of 1000 miles across the Gulf Stream and back. A total of 52 miles of lateral drift was corrected to produce a straight line of travel through the observed currents, and this correction enabled the ship to return to within 2 miles of the starting point. Seven less formal experiments performed in 1950 indicate that ordinarily, on straight-away courses, the lateral drift component caused by currents can be measured and corrected with the expectation that the undetected drift will be less than 1 percent of the distance travelled.

The three basic problems of navigation are determination of position, definition of direction, and steering the direction required. In polar regions, all these problems are affected either by the high latitude, or by the polar climate, or by both. In this paper the various problems which arise are reviewed, possible solutions are discussed, and it is indicated where further research and experiment might be desirable.

The Earth's magnetic field can evidently be divided into its horizontal and vertical components, the horizontal component being of more immediate interest to the navigator since it directs the compass needle in the horizontal plane. Whereas on the magnetic equator the full field is horizontal (about 0·400 c.g.s. units), in high latitudes, with the angle of dip between 60° and 70°, H, the horizontal force, maybe about 0·180 c.g.s. units. At the magnetic pole H is negligible and, given the opportunity, the compass needle would point vertically downwards, the instrument then having no directional properties in the horizontal plane.

The use of radar in relation to the Rule of the Road at sea is a subject over which there is still a great deal of controversy. An examination of the main problems involved was made in this Journal (Vol. 3, No. 1, January 1950) by Captain F. J. Wylie who concluded in his paper that the use of radar might justify a more liberal interpretation of the term ‘moderate speed’ than has hitherto been countenanced; and a recent amendment to the King's Regulations and Admiralty Instructions clearly accepts the use of radar as an existing circumstance within the meaning of Article 16.

No attempt, however, has so far been made to arrive at a precise definition of ‘moderate speed’, and it may well be that the reasons which prevented a definition being made in the non-radar case are in fact given more force when radar, with its added variables, is used. On the other hand it is unlikely that any progress in the matter can be made without a full discussion of the factors involved, and Captain Robb's paper, though it may be possible to dispute some of his conclusions, is presented here as an interesting attempt to achieve a definition which can serve as a guide to shipmasters.—Ed.

In a recent paper on shipborne radar the authors tried to analyze the mental approach of a master or pilot to the problem of handling his ship in a confined space when berthing in fog. The sense of loss that is caused by the absence of direct vision was referred to and various means by which confidence and control might be restored in these circumstances were considered. In that paper only the inadequacies of present-day shipborne radar in meeting these requirements were discussed. The approach to the problem can, however, be broadened to include the whole question of port operation in fog, and the present paper attempts to describe the general requirements and to consider in particular the role of shore-based radar and the manner in which the information obtained from radar or other aids should be presented to the master.

It is difficult to get satisfactory noon observations when the zenith distance is very small, because the Sun is rapidly changing in azimuth, the sextant must be swung through a wide arc of the horizon, and the Sun only dwells at the highest altitude for a very short period. To avoid these difficulties it is suggested that, instead of trying to measure the altitude of the Sun, one should measure its distance from a point on the horizon in a known azimuth. To make this measurement the Sun is brought down to the required point on the horizon, tilting the sextant as necessary; we shall distinguish this type of observation from the normal one, made with the sextant vertical, by calling the angle so obtained the horizon distance. At normal altitudes this method, however sound in theory, breaks down because one cannot measure the azimuth with sufficient accuracy. However, at very high altitudes the rate of change of horizon distance with change of azimuth of the point from which the distance is measured becomes so small that it is not necessary to know the azimuth with such precision. In fact, at a zenith distance of 1°, the largest we shall consider here, the greatest error caused by an error of 1° in the azimuth is l″, and for smaller zenith distances the maximum error is proportionately less.

This paper is an appreciation of the navigational problems encountered during a flight round the world in 1948, in a single-engined light aircraft. The route chosen (Fig. 2) covered nearly every type of flying weather in the world, from the perfect conditions of the Mediterranean in the summer to the severe climate of the Aleutian islands; navigation tests were provided by the overwater flights across the South China Sea (Hong Kong—Okinawa = 900 miles), the North Pacific (Chitose—Shemya = 1730 miles) and the North Atlantic.

A condensed version of a paper presented to the Centre Beige de Navigation, Brussels, 9 January 1950.

The fact that the most expeditious route between two points on the Earth's surface is not necessarily a great circle is no new discovery. In the days of sailing ships courses were set to take maximum advantage of the wind; the trade winds were so called because they made the voyages of the trading ships possible. To a large extent they dictated the sea lanes and it was not until the arrival of the steamship that more direct routes across the oceans could be followed.

The British standard blind flying panel and its component instruments have for many years fulfilled a very useful purpose, but there are now a number of special operational requirements which this panel no longer meets. For instance, the probable general use of tail warning devices will make it necessary for the night fighter pilot to follow the violent evasive action of his quarry, and because of the higher speeds involved it is desirable that the pilot should be able to interpret his radar scopes himself rather than depend upon his navigator for directions.

Members will have learned with regret of the death of Dr. L. J. Comrie, M.A., PH.D., F.R.S., who died at the age of 57 on 11 December 1950. Dr. Comrie's contributions to science were primarily in the fields of astronomy and computation, and in the latter field he may be said to have created the modern concept of scientific computing and to have laid the foundations for the present widespread interest in numerical methods and in digital calculating machines. Tributes to this side of his work have already been paid, both here and abroad, and the Royal Society and the Royal Astronomical Society are both publishing fuller notices which will give a detailed assessment of his work. The following note, pays a tribute to Dr. Comrie's contribution to navigation.