When designing the periscopic sextant now coming into production it was realized that the conditions in the pressurized aircraft for which this sextant was designed differed sufficiently from those previously experienced to make it worth while reconsidering what methods would be most applicable to the new combination of pressurized aircraft and periscopic sextant.

The conditions differ from previous experience in providing (a) a higher speed; (b) very little, if any, direct view of the sky by the navigator.

Throughout the history of marine navigation it has been recognized by seamen that soundings of the sea bed are a most natural and valuable aid to safe passages. Yet it is probably true to say that the methods of obtaining such soundings and for recording and using the information so obtained remained relatively primitive for longer than any of the other arts or systems used by seamen.

Records can be found which indicate that the earliest navigators used poles or lines and plummets to measure the depths of water on the coasts and in the rivers. An example of the use of soundings by Phoenician seamen is recorded by Strabo, who relates that the captain of a Phoenician ship on a voyage to the Casseterides for tin thought himself too closely followed by a Roman ship and deliberately sought a shoal which he knew of on which to run his vessel to avoid capture and the loss of his precious secrets. Then Hanno, the famous Carthaginian admiral of about 500 B.C., at his furthest point south on the West Coast of Africa, outlined the contours of the River Niger, and the Greek admiral Nearchus at the same time made his voyage from the Indus to the Euphrates by soundings in the rivers and on the coast.

During a cruise by H.M.S. Fleetwood in Scandinavian waters last autumn the opportunity was taken of measuring the intensity of echoes received from the sea, for various wave heights. These echoes are commonly known as sea clutter and the object of the measurements was primarily to provide data on which to design suitable anti-clutter circuits for use in civil marine radars. The results obtained, however, show the need for increasing the radar echoing characteristics of small navigational marks and small boats.

If astronomical navigation is only required to give a ten-mile accuracy, as Mr. Parker has suggested in his paper, then its use will be mainly that of a last-aid in emergency. Radio, however, will give this degree of accuracy and, since a radio operator will in any case be carried, will naturally be more popular. On the other hand if astronomical navigation can be made to give a ½-mile accuracy it will become immensely more valuable than any other long-range aid. In the first place the signal received from the stars is completely reliable (at the heights which concern the air navigator, variable refraction can be ruled out) ; it is wholly independent of the ground; it provides a universal coverage which is free and is controlled by a non-political Body; and it can provide an accuracy greater than that of the long-range aids except the limited-purpose systems such as Oboe.

In this note, we propose to enquire into how far it may in principle be possible to employ zenith-photography for astro-navigation in the air, also to touch on the question of whether the mechanical difficulties can be adequately overcome. The question of principle seems in fact quite clear, but the practical side will undoubtedly demand much care and study by engineers and by practical navigators if the method is ever in fact to be adopted; we hope to show that the method has advantages sufficient to make the problem worthy of attention.

No satisfactory means of securing positive identification of individual radar echoes in congested waters has yet been devised, although many ingenious suggestions have at different times been put forward. These ideas include systems for providing a special identification signal from selected buoys, or alternatively for a considerable increase in the number of buoys and their arrangement in groups in definite patterns at strategic points so that they may be easily picked out on the ship's P.P.I.

In the discussion on Blind Estuary Pilotage held by the Institute on 18 June 1948, the writer (see Journal, Vol. 2, No. 1, p. 60) put forward the suggestion that the well-known principle of radar shadowing could be used to provide accurate leading patterns for ships navigating straight channels or harbour entrances. Two possible patterns of this sort are illustrated in Figs. 1 and 2.

The pattern shown in Fig. 1 uses six ‘targets’ and two ‘screens’ and would be suitable for any channel wider than about 200 yards. The channel illustrated is meant to be about 200 yards wide, and the configuration of the pattern—though not the dimensions of the targets and screens—is drawn to the same scale.

Static electrical charges from the atmosphere can in certain circumstances become attached to an aircraft in flight. This can prove dangerous to flight if radio aids to navigation are being relied on as the electrical charges result in precipitation static interference. The phenomenon was at first confused with the interference to radio resulting from transient atmospherics, although precipitation static interference is in fact largely of a continuous nature.

If astronomical navigation can be made to give its results in as simple a manner and as quickly as do the modern electronic systems, then clearly it can provide an aid whose usefulness will remain undisputed. The aim, then, should be to develop a system of astro-navigation which will give an immediate and continuous reading of, for instance, latitude and longitude; and it seems quite possible at the moment to envisage the nature of such a system. Its realization is perhaps another matter; and this may take time that perhaps the development of other systems will render ill-spent.

The ideas put forward in this paper are only concerned with the fundamentals of what, in the writer's opinion, is a possible solution to the problem; they are also not all new.

It seems probable that the magnetic compass, the mariner's compass as it is often called, first made its appearance at some time between the tenth and twelfth centuries A.D. Attempts have been made to prove that the compass was in existence earlier, and that some of the early voyages could not possibly have been performed without its help; but there is no evidence to support this contention and a certain amount to show that other methods were used.

Again, it has been suggested that some obscure remarks by certain classical writers could be explained if the author were assumed to be describing the use of a compass, whilst having only the haziest notion of what it was. Among such is the legend of Abaris, the Hyperborean priest, who visited Greece, some say from Britain, many centuries B.C., and had with him a mysterious arrow which showed him the way. If we cut out the fancies of some writers who credited him with the possession of a kind of aircraft (capable of supersonic speeds), it is not difficult to imagine that the arrow may have been a magnetized needle. The difficulty is in understanding how no one down the centuries which followed came to write of the compass. There is, of course, little doubt that much scientific knowledge was possessed by the ancient priestly cults and the knowledge of the compass may have been kept secret for their own ends. If the great library of Alexandria had not been destroyed we might have had the answer to the riddle; but perhaps there is none and the whole tale of Abaris is a fabrication.

Some questions affecting the operational value of shipborne radar and on which there is, at the moment, no clear unanimity of view are discussed in this paper.

The best position for the console is discussed in the light of requirements which vary with the different uses to which a shipborne radar can be put. The advantages of a chart comparison unit are also considered and the conclusion is drawn that these can be more economically gained by other methods. In particular the use of P.P.I. photographs is advocated as a method of land echo identification which leaves the chart free for other uses.

At the request of the Ministry of Transport and the Humber Conservancy Board, a visit was made to the River Humber in H.M.S. Fleetwood to determine whether the navigational marks at present in use would be suitable for pilotage of the river in poor visibility by a ship fitted with a U.K. radar.

P. F. Everitt (Journal, Vol. 2, No. 1, p. 49) has discussed the problem of precomputing sights but gives the impression that the A.N.T.s cannot be used for this purpose; this is not the case, provided of course that the accuracy of 1 or 2 miles obtainable from A.N.T.s is acceptable. My experience of the method described below is confined to marine use with Hughes' Tables, but the same limitation of being confined to integral degrees of latitude and hour angle applies, so the method is clearly applicable in the air. Provided that the observation is actually obtained, the extra work involved in computing the sight in advance is trifling, and there are often appreciable advantages.

This paper is confined to a non-technical survey of the particular application of radar to the maintenance of a fast schedule of ferry vessels operating across a busy tidal river. After some seventeen months' practical experience of this application it is possible to give some opinions of the value of radar as a commercial aid to navigation.

Wallasey Ferries operates a twenty-four hour service between Wallasey and Liverpool, and carries some twenty million passengers per annum.

For the purpose of comparing results with the two wavelengths, 3 cm. and 10 cm., generally used in navigational radar, the Defence Forces Research Institute, in collaboration with the Swedish Admiralty, the Royal Pilot Service and the Marine Cartographical Institute, carried out systematic researches and experiments under various conditions, in view of the special meteorological and navigational circumstances prevailing in Swedish waters. Two radar equipments covering these wave-bands were obtained from the Research Institute and installed on board the marine survey ship Gustav Av Klint during the summer of 1947. A separate report has been issued on the results obtained during the summer months.

This paper described how 53 ships of the United States Lines had been fitted with 10 cm. radar and how instructions for maintenance and operation were given by the Company and the manufacturers of the equipment. Instruction in its use is given by a representative of the manufacturer, and subsequently minor adjustments and fuse replacements are made on board, all other maintenance being done under service contract in port.

General instructions sent by the Marine Superintendent to the Master of each vessel fitted stressed the following points:

1. i. For the present the equipment is to be regarded solely as a collisionwarning device.

2. ii. The installation in no way relieves the Master from conforming to the Rule of the Road or any Pilot Rules.

3. iii. A complete radar log in which maintenance and operational work are recorded should be kept.

4. iv. Deck officers should acquaint themselves with the use of the equipment and should be encouraged to read the manufacturer's descriptive and operational booklet.

In present designs of radar sets for merchant ships, the radar-equipped ship is represented as being at the centre of its own P.P.I. picture. But there is a case for having an off-centre display. In this article are discussed possible advantages to be obtained from such a display, when the set is being used for collision warning away from a coast-line. The author recognizes that some of the opinions expressed are of a controversial nature.