The most attractive features of Lieutenant-Commander R. B. Michell's method of plotting astronomical position lines with a ‘star lattice’ are that (a) plotting, relative to the moving D.R. position, is possible immediately after the sight is taken; (b) the whole process is continuous.

The following account of the U.K.–New Zealand Air Race was given to an Institute meeting on 20 November 1953 by members of the Royal Air Force Race Team. The lecturers were Wing Commander L. M. Hodges, D.S.O., D.F.C, who commanded the R.A.F. flight, Squadron Leader R. Currie, A.F.C., chief navigator of the flight, who flew with Wing Commander Hodges, and Flight Lieutenant R. L. E. Burton, A.F.C., pilot of the Canberra which completed the course in the shortest time; the Chair was taken by Air Chief Marshal the Hon. Sir Ralph Cochrane, G.B.E., K.C.B., A.F.C.

At the time (1542) when Jean Rotz presented Henry VIII with a variation compass, and an accompanying treatise1 on its making and use, the question of magnetic variation was an acute one. It formed part of a wider controversy concerning the general validity of the sea-chart which had been raised among seamen. As to this, Dr. Pedro Nuñez, writing a treatise in 1537 addressed to his friend and pupil the Infante Dom Luys of Portugal, said that there were skilled pilots who derided the chart and declared it to be ‘a mais falsa causa do mundo’—the falsest thing in the world. Hastening to its defence, Nuñez dealt at length with the navigating errors introduced by ignoring the convergence of the meridians, and showed besides that a rhumb, or line of constant bearing, was a spiral curve on the globe. He dealt only incidentally with the variation of the compass needle and how to measure it, and this may explain why Rotz made this second source of error his main theme. The parallel N.–S. lines and E.–W. lines of the compass roses making a rectangular net on the chart are completely misleading, he says, for only the ‘diametral line’ (agonic line, line of no variation) actually runs through the poles of the world, the others lie at angles one with the other according to the magnetic variation.

Few aspects of geography are more satisfying than to follow the progress of geographical discovery across the oceans from the documents that remain to us, and the careful work of many scholars allows us to find some of the excitement of the early voyages without much effort to ourselves. But geographical exploration was only the first phase, and during the past 300 years much effort has been spent in finding out something about the oceans themselves: as early as 1698 Halley sailed as far as S. 52° on a purely scientific voyage, returning with useful information about magnetic variation and the trade winds. The promoters of the scientific voyage of H.M.S. Challenger argued that the vast oceans lie scientifically unexplored, and we say much the same today; but much has been done and in its way it provides a story as interesting as that of geographical discovery.

This paper is concerned with measures which may be used to reduce the effect of echoes from the sea surface and from rain (sea and rain clutter) on radar displays so that targets which give a reflected signal power greater than the reflected clutter power can be detected. It should be noted that a conventional PPI display is fully brightened by signals of amplitude about three times the level of the inherent noise background, so that once the clutter has exceeded this limit it will appear on the display as a fully bright patch in which signals can be lost, even though their amplitude at the receiver input may be many times greater than the amplitude of the clutter.

In about 1946 work was begun both in the United States and in the United Kingdom on the development of radar beacons which could be used to make certain required points more conspicuous and to increase their detection range.

Two basic types of beacon were considered: ramarks, which are intended to give bearing information only and which appear on the PPI as a bright radial line passing through the position of the ramark, and racons, which give range as well as bearing information. The range information is given by die beacon transmitting one or more short pulses, the first of which appears on the PPI at the correct range and bearing of the beacon.

When harbour surveillance radars were first fitted in the United Kingdom in 1948 it became apparent that under conditions of high traffic density difficulty might arise in identifying the ship being assisted into harbour with a particular echo on the radar screen. The group at the Admiralty Signal and Radar Establishment (A.S.R.E.) working on navigational aids for the Ministry of Transport were set the task of examining the problem and suggesting a solution, and this paper will describe the results of this work.

It was with some surprise that I read Commander Sharpey-Schafer's ‘Some Notes on Astronomical Observations at Sea’ (this Journal, Vol. VI, p. 362), especially his conclusions regarding the fixing accuracy obtainable with marine sextant observations. I can makeno claim to be an experienced navigator myself, but, as a member of the staff of H.M. Nautical Almanac Office, I was privileged, in 1949, to spend three months as an observer on board H.M.S. Dalrymple, a newly-commissioned surveying ship, under the command of Captain (now Vice-Admiral Sir) A. Day.

Vice-Admiral Sir Archibald Day, the Hydrographer of the Navy, who was chairman at the Institute discussion on 15 May 1953, has received the following comments from Rear-Admiral Robert W. Knox, Assistant Director of the U.S. Coast and Geodetic Survey.

To quote the Collision Regulations—‘Risk of collision can, when circumstances permit, be ascertained by carefully watching the compass bearing of an approaching vessel.’ Most seamen are so familiar with this injunction and with the practice it describes that any particular significance in the wording probably escapes them. It is, however, important in considering the operational use of radar to note that the compass bearing and no other kind is specified and to appreciate that this is so because the relative bearing will only give quite comparable assurance when own ship maintains a perfectly steady course during the approach.