The seaman requires of radio aids to navigation that they should be effective substitutes for astronomical and terrestrial methods of fixing when these fail him, either wholly or in part. For normal peacetime voyaging there has been no firm demand for a radio system that will improve on the performance of the other methods at their best. The requirements for radio aids can therefore be related to the facilities which these other systems afford. This does not, of course, imply that circumstances do not exist in which radio aids can provide a degree of assurance that the other methods might not.

Presented at a meeting of the Institute held at the Royal Geographical Society on 15 June 1951.

Shore-based radar stations to supervise or assist the navigation of ships have now been employed for at least a decade. Such stations were more extensively used during the war than they have been since, principally because there had to be large convoy movements along heavily mined coastlines under conditions when, because of wartime limitations, many of the more conventional navigational aids were not available. The most important wartime development in the use of radar in this direction was undoubtedly the introduction of high power centimetric equipment and the plan position indicator. Since the war the use of shore-based radar to assist navigation of merchant shipping has been extremely limited and the only outstanding installation of this type is the Liverpool Harbour Supervision System, which was brought into service in 1948. This system has now been in operation for three years and has provided a great deal of information and has created a world-wide interest.

Sailors as a class may fairly claim to have been the earliest technicians; they were the first, that is to say, to graduate from the stage of simple craftsmanship, involving only the use of tools and rules of thumb, to the employment of instruments and mathematics for solving their problems. For the nautical chart and magnetic compass are instruments of precision while sailing directions, if they are to be useful, must be couched in mathematical language. All these three aids to navigation go back at least seven hundred years, and an Italian ship inventory of 1294 has been quoted which included two charts, a pair of compasses and two lodestones with their accompaniments.

Reference to a chart of the Thames Estuary will show that the dominant feature of the submarine morphology is the series of elongated banks, of which the Barrow, Sunk and Long Sand are the most important. Between these banks, and with the same north-east to south-west trend, are the navigable channels of the Swin, Barrow and Black Deep (Fig. 1).

The alignment of the channels suggests that they originated as a result of tidal-stream scour of a fairly uniform sheet of fine silt and sand. In each tidal period, streams enter the estuary from the north and flow on the flood in a south-westerly direction parallel to the Essex coast. After about six hours they slacken, turn and flow out of the estuary in the reverse direction. This continuous flood and ebb stream action, with a maximum velocity varying from 2·3 to 2·9 knots depending on whether the tide is neap or spring, has apparently scoured out channels to depths which exceed 10 fathoms in places. If the channels largely arose in this way, the banks represent the modified remnants of the initial surface. These banks are constantly being extended seaward as more riverine silt is emptied into the estuary by the Thames, Medway and the rivers of Essex. The distal end of Long Sand alone has grown almost ½ mile in the past 100 years (see Figs. 1 and 4).

Over thirty-seven years have passed since the writer published his ‘Wrinkles in Plane Chart Methods’, explaining the value and use of his then new ‘Protractor Diagram’ and ‘Graduated Triangle’ for plotting lines of position on squared paper. A figure showed the simplicity of the solution, overcoming the difficulty of the use of different units for the differences of latitude and longitude.

It is now proposed to present a further ‘wrinkle’ to facilitate the use in navigation of six prominent equatorial stars, particularly Mintaka (δ Orionis) which is only 2o′ south of the equator, and practically a fixed star since its annual (precessional) variation in declination is only 2″·67. It is one of the three stars of Orion's belt and its magnitude is 2·5, slightly fainter than Polaris.

The Abridged Nautical Almanac in its revised form, for the year 1952, has now appeared. In place of right ascension and the familiar quantities E and R which were adopted in 1929, it tabulates Greenwich hour angle in arc for the Sun, Moon, planets and Aries, and sidereal hour angle (or versed ascension) for the stars.

Greenwich hourangle has been used in air almanacs for a number of years, and several surface almanacs have tabulated it as an alternative to right ascension; it is only recently, however, that it has been given exclusively in surface almanacs. Among the surface almanacs which tabulate G.H.A. at present are the American, Spanish, Argentine, Brazilian and Yugoslav.

The redesign of the Abridged Nautical Almanac has been under consideration for many years, but the change was delayed first by the war, and then by the desire to avoid a transitional period during which the new G.H.A. and E and R were given together; it was also decided to give as much notice of the proposed changes to users as possible. The design in substantially its present form was in fact accomplished in 1947, though the arrangement of the daily pages and much detailed work was carried out later.

As from 1953 the Air Almanac and the American Air Almanac will become a single publication, under the title of the Air Almanac. It will be produced jointly by H.M. Nautical Almanac Office of the Royal Greenwich Observatory, Herstmonceux, and the Nautical Almanac Office of the U.S. Naval Observatory in Washington, to meet the general requirements for air navigation in the United Kingdom, the United States and Canada. The Air Almanac will be printed and published separately in the United Kingdom and the United States but the two publications will otherwise be identical.

Summary of a paper presented by Dr. Bowen, as President of the Australian Institute of Navigation, to a meeting of the Institute held on 15 June 1951.

Accounts of the work described in this paper have been separately published, many of them in this Journal. The paper, therefore, restricts itself to giving a summary of this work, referring the reader to the appropriate literature for further study, and to pointing to some of the outstanding landmarks over the last few years.

The work referred to has been carried out by the Radiophysics Division of the Commonwealth Scientific and Industrial Research Organization in Australia and falls conveniently into two main headings, dealing with short-range aids to navigation and with air traffic control. It has been conducted for air navigation, but one at least of the navigation aids developed may find a useful application for maritime use.

Summary of a paper presented to the Canadian Institute of Navigation at a meeting held in Montreal on 22 September 1950.

In 1946 and 1947 a great deal was learned about scope interpretation and the use of search radar as an aid to air navigation in the Canadian Arctic. New techniques, differing from those used during the war, when search radar was considered primarily as an aid to bombing and for pin-pointing, were developed and a great deal of information on interpreting the radar presentation of topography at different seasons was obtained. The use of search radar for navigation in the Arctic is described in this paper, which also gives information on the probable appearance of topographical detail on the display at different times of the year.

Soon after the introduction, in March 1947, of GCA to London Airport, it was realized that the advantages which it had brought to approach control could be greatly increased if the range of the radar could be extended to give earlier and more accurate information to the flight information controllers, and eventually the airways controllers, on the position of aircraft. At the time when the Ministry of Civil Aviation had installed and were testing an MEW type radar at the west end of London Airport, the question of the extended cover required from radar in this country was under active consideration. It was thus planned to develop long-range radar control techniques and procedures to be used in conjunction with the MEW radar. The work was planned to fall into three separate stages: (1) experiments in combined MEW/GCA working (termed long-range GCA); (2) operational trials; (3) operational service.

The traffic control arrangements of the Royal Aircraft Establishment, Farnborough, although they have never been the subject of intensive operational research, but have been derived by a process of steady growth, may be of interest as an example of what can be achieved by good organization on an ad hoc basis under some of the most difficult operational conditions.

The Royal Aircraft Establishment has an experimental airfield situated in a highly congested area. The London control zone and area is immediately to the north and east, and it is fringed on three sides by civil traffic lanes (Green Airway i in the north and north-west, Red i in the east, and the proposed Red 2 in the south). The Blackbushe circuit of the Ministry of Civil Aviation inter-locks with the Farnborough one in the north north-west, and the circuit of the Odiham R.A.F. airfield, from which jet aircraft are regularly operating, is situated only five miles away in the line of the main bad-weather runway.

A Letter published in the Journal (Vol. IV, No. 2, p. 211) from Captain Brett Hilder refers to the use of the phenomenon known as the green flash for obtaining longitude at sea, and an editorial comment on the letter suggests that accurate descriptions of what has actually been observed at different times at sea might be of value to meteorologists. The following notes, though they contain no reference to using the observations for navigational purposes, may be of some interest as they are the result of a great many observations of the phenomenon.

Numerous reports on observations of the green flash have been published in meteorological publications where, as a general rule, it is accepted that it is only seen under conditions of extreme visibility and clearness of the atmosphere. From numerous personal observations it has been ascertained that this is in fact not so, and that the green flash can be observed under conditions of extreme cloudiness, haze and humidity so long as the horizon is visible at the time of rising or setting of the heavenly body. Another factor affecting the actual sighting of the green flash is the intensity of light emanated by the body, for the flash is of very weak intensity when compared to the normal brilliance of the body observed.

The method of taking high-altitude observations at sea described by A. N. Black in the April number of the Journal is not widely known and is undoubtedly of practical value, though it is not new. In his article Mr. Black regretted that he had had no opportunity of testing the method under practical conditions as his cruising range did not extend into the tropics. For this reason the results of some actual observations taken by the present writer some twenty-five years ago using this method may be of interest to Mr. Black and to readers of the Journal.

The author is in entire agreement with the first ten lines of Mr. Black's paper, though the term slant altitude or inclined altitude might express better what is being measured than horizon distance, which may be misleading. He does not however agree that the method is sound in theory for ‘normal’ altitudes, as will be explained. The method is in fact both practically and theoretically restricted to use with zenith distances of about i°, which is the limit actually considered in Mr. Black's paper.