In 1952 the Institute set up a Working Party, under the chairmanship of Mr. D. H. Sadler, to investigate the accuracy attained in the practice of astronomical navigation at sea. The report that follows was presented in summary to the Technical Committee on 15 February, 1957, and formed the subject of a discussion at the Institute's meeting on 21 June.

The following conclusions relate to a total of 424c, observations received by the Working Party from 173 observers, and are representative of navigational practice as a whole only in so far as the observations, and the observers, are so representative. Only 3319 observations from 1 r6 observers were retained as suitable for analysis, and in nearly half of these observations the ship's position is not known sufficiently accurately for them to be included in the main analysis.

The objects of the International Geophysical Year have been fully described in the Journal. The idea itself was first conceived in 1950 at a social gathering in the home of Professor J. A. van Allen, in Maryland, U.S.A. The small group included Professor Sydney Chapman of Great Britain and Dr. Lloyd Berkner of U.S.A., now respectively the President and Vice-President of the special committee for the International Geophysical Year. They considered that recent advances in geophysical science were such that an interval of fifty years, such as lay between the First and Second Polar years, would be too long. Moreover an interval of twenty-five years from the Second Polar Year would coincide with a period of maximum sunspot activity. Later in the same year the International Council of Scientific Unions adopted the idea and in the following year set up the special committee; at the same time the nations adhering to I.C.S.U. were invited to form national committees, of which there are now more than sixty. Their programmes make up the vast international world-wide effort. A duration of eighteen months, July 1957 to December 1958, for the Year was agreed.

At the present time with the increase of air traffic across the Atlantic (and still more so in the future when jet aircraft will be numerous) it becomes very necessary to know what is the safe separation between aircraft, and whether some form of controlled paths may not economically be imposed between America and Europe.

Some meteorological offices now include isotachs (lines joining points of equal wind speed) on forecast upper-air charts for long-range flights. Heretofore, dispatchers and aircrews have been obliged to measure winds from upper-air charts displaying contours only. This meant use of a geostrophic wind template, and correction for cyclostrophic component and latitude. The new contour-isotach charts, in addition to displaying wind speeds more readily, present greater accuracy, since they are determined by forecasters, who may call upon better theoretical know-how, and later observational data. In order to take full advantage of this improvement, Trans-Canada Air Lines has developed two new templates; one for route analysis (determination of the best-time track) and the other for flight planning. These are designed with ease of production in mind as well as simplicity in use. They are produced photographically on heavy film, and have no moving parts.

People often think that early seafarers must have clung to the coast, but there is plenty of evidence that from the earliest times seamen have not only ventured out of sight of land but have conducted regular passages across the open sea. No doubt, however, landmarks did provide the earliest aid to navigation and in the eastern Mediterranean where the science was born, ships would not have been out of sight of land for more than a day or two.

If a navigator wishes to determine the closest passing distance of his ship to any other ship by means of radar, it can be done quite simply by plotting the ranges and bearings of the other vessel's echo. The line joining the plotted positions will indicate the relative course of the other vessel and by extending the relative-course line the closest passing distance can be measured. With the existing method of measuring bearing by means of a mechanical cursor with its attendant possible in-accuracies, it is necessary to plot a number of positions and draw the relative-course line as a mean through the plotted positions. The time taken to establish the nearest approach is therefore comparatively long. If an electronic bearing cursor is used the time to determine the nearest approach can be reduced since the accuracy of the measured bearings will be higher, and fewer measurements required. It may, however, be inconvenient to move from the radar screen to the plotting table and if plotting is done on the face of the PPI or a reflection plotter, the accuracy may be poor, particularly if the nearest approach is determined by extending a relative-course line formed by two plotted positions close together, using a blunt wax pencil.

Over the better developed land areas of the world, where radio and communication facilities enable aircraft positions to be known on the ground, the system of Airways flying has been introduced. In areas of high traffic density it is of the greatest value, as it allows the traffic control authorities to separate aircraft at moderate to close intervals. The system requires good and continuous radio track guidance and a regular reporting procedure at specific radio fixes. (Airways are normally looked upon as fully controlled areas and until some more reliable long-range aid which can present continuous fixing is developed, Oceanic Airways would be more properly referred to as Oceanic ADR's.)

The weather at an airport affects the ability of an aircraft to land in so far as it controls the pilot's vision of the runway as he approaches it. This aspect of weather is at present described by (a) Runway Visual Range (RVR) as measured along the runway by Air Traffic Control, (b) Visibility as measured from and by the Meteorological Office, and (c) the amount and height above the airfield of the lowest cloud. Weather minima are specified in terms of RVR or visibility and of cloudbase by each Company for each type of aircraft using each available type of approach aid on each runway at each airport, such that an aircraft should not try to land in worse conditions. A landing forecast known as a TAF is issued regularly for each airport and specifies among other things visibility and cloudbase, giving either single values for each, or subsidiary ‘possible’ values indicating temporal variations or values with a small probability of occurrence. Examples are: ‘Visibility 10 miles TEMPO (temporarily) showers Visibility 2 miles’. ‘Fog Visibility 500 yards GRADU (gradually becoming between) 0400–0600Z mist Visibility 1 mile’. The TAF for the destination is seen by the aircraft captain before departure and during flight: if it is unfavourable he may decide to increase the fuel reserve reducing the payload or to delay departure or to divert. A wrong TAF may have costly and occasionally dangerous results.

The suggestion in this note is the result of reading D. E. Adams's paper on inertial navigation (this Journal, 9, 249) and Captain Maya's paper on dead reckoning (this Journal, 10, 84).