This paper describes a method for the reduction of simultaneous star altitude observations in pairs, whereby an unambiguous ‘fix’ is obtained without reference to the dead reckoning position and without use of the intercept procedure. The method is adequate in all latitudes. An especially swift reduction is possible for the moments at which two stars are situated at equal altitudes.

When position is determined by means of two simultaneous star altitude observations and use is made of a single chosen position it is possible for the Marcq St. Hilaire intercepts to be so short that they can be regarded as negligible. When this occurs the chosen position is, in effect, the true position as indicated by the observations and no further work is required for a fix. If, in such a case, it is desired to have the Sumner lines of position represented on the chart it will be possible to draw them through the chosen position. The selection of such a chosen position may be made with certainty, in every instance, by computing numerical values for the latitude and the longitude of the appropriate intersection of the two circles of equal altitudes corresponding to the corrected observations. If the entire computation had to be done after the observations were made, the labour of this procedure would prohibit its use in rapid navigation. It happens, however, that the greater part of the work can be precomputed and presented for the navigator's use in a tabular form. These data are extremely compact and are permanent except for the need of occasional adjustment for precessional effects and on account of proper motions of the stars. No almanac would be required for use with such a table if the navigator were not dependent on it for his G.H.A. Aries. No knowledge of the dead reckoning position is employed in this computation; star observations suffice to determine the position without ambiguity.

In his Presidential Address to the Institute this year the Astronomer Royal, Sir Harold Spencer Jones, stresses the importance of an early resumption of the general survey of the Earth's magnetic field and developments in airborne magnetometers in the United States have suggested the possibility of using aircraft for this purpose. The techniques which are available for aerial survey will be discussed in this paper and an attempt will be made to evaluate the relative merits of conducting world wide magnetic surveys by sea and by air.

This paper is concerned primarily with an investigation of the loxodromic distance between two points on the spheroid. This is derived by a modification of the meridional parts method in terms of the track angle and the difference of latitude reduced by a correction which is a function of the latitudes concerned.

Since the method is unsuitable when the track angle is near to 90°, the known formula for the mid-latitude correction is examined and an alternative method suggested for use in this case.

The results obtained are compared in a practical example with those found by the usual methods, and finally means are proposed by which the refinement described above can be incorporated into current plotting practice on aeronautical Mercator charts.

An abbreviated version of a paper read before a joint meeting of the Institute and the Royal Aeronautical Society.

The usefulness of a particular aircraft may well depend upon the availability or simultaneous development of equipment. Safe, reliable, economic and speedy operation in the civil field may rest, for instance, on facilities which enable all-weather operation to be undertaken—including navigation, traffic control, approach and landing facilities. Military operations, even more directly, will be determined by the instrument aids available.

In this paper two collision cases and four cases of ships grounding will be examined and the circumstances analysed with a view to drawing some useful conclusions from them. In the case of the collisions no general theory can be advanced but they both have a navigational interest from the point of view of the International Regulations Jor Preventing Collisions at Sea and a certain amount of useful comment can be made on them.

The King William Banks buoy is situated about 12 miles east of the northern tip of the Isle of Man. It marks the eastern extremity of the bank of this name and is an important turning point, especially for the British Railway ships on the Heysham to Belfast run. This buoy, which is unlit, is a third class spherical buoy and thus presents a poor radar target. The British Railway ships are fitted with radar and always pass the buoy at night so that if it could be detected by radar regularly it would be of great assistance to navigation. In fact complaints were made about its radar reflecting properties, and accordingly a pentagonal cluster of 12 in. corner reflectors designed by the Admiralty Signal and Radar Establishment was supplied to Trinity House and mounted on the buoy on 3 March 1949 (see Notice to Mariners 619/49) at a height of 11 ft. 6 in. above the water.

Probably the most important single factor governing the value which can be obtained from a given radar equipment in a ship is the presence or absence of blind or shadow sectors. This is entirely dependent, on the siting of the scanner. There is no arc of bearing on which the careful seaman does not keep a visual lookout, constant or periodic, when his ship is at sea. As radar is capable of providing him with a means of detection on all bearings, which will often be more effective than his eyes, it would be surprising if he were not prepared to go to some lengths to avoid obstructions to its ‘view’.