Every navigator is familiar with the necessity for correcting sextant observations of altitude for the effect of atmospheric refraction. He does this by means of tables which the great majority of navigators are compelled to take on trust, as they would a table of haversines. Unfortunately it is much easier to guarantee the accuracy of a table of a straightforward mathematical function than it is to tabulate accurately an optical effect occurring in a notoriously variable atmosphere. Recent American work based on large numbers of marine observations has to some extent called into question the accuracy of the low-altitude portions of the usual tables, and it therefore seems worth while to give a brief account of refraction theory and also to consider how far it is confirmed by observation. The treatment will be restricted to refraction as it affects marine navigation. This is a considerable simplification. Aerial observations may be made at any level between the ground and the lower stratosphere, so that air navigation involves a much greater range of pressures and temperatures at the position of the observer. Moreover, it involves some occurrence of much more strongly negative altitudes than can be observed from bridge height on a ship, and at such negative altitudes (i.e. zenith distances over 90°) the intrinsic variability of the refraction is large enough to make any table rather unreliable.

The usual method of using radar for navigation at sea is to transfer the information from the PPI to the chart. In many instances, however, the pilot will con the ship directly from the PPI, using his local knowledge, which is equivalent to using a chart impressed on his mind. In such cases it is necessary to identify immediately and unambiguously the PPI paints, which often bear little resemblance to the shape on the chart of the feature which is producing the echo.

The year 1952 is the fourth centenary of the birth of Sir Walter Ralegh. So far from being the great romantic of tradition Sir Walter was a hard-headed practical man, and the first Englishman to engage a scientific and technical expert to advise him on his colonizing enterprises. He brought the brilliant young mathematician Thomas Hariot, some eight years his junior, direct from Oxford to Durham House, his mansion in the Strand, where, setting his instruments up on the leads, Hariot laboured for years at improving observational technique and revising the Ephemerides. Meanwhile he gave instruction in navigation to the officers of Ralegh's ships, himself obtaining practical experience on the voyage to Virginia in 1585, when he was able to observe the seaman's difficulties and the errors to which he was prone. He had already by 1584 written a new Instruction Manual which he entitled Arcticon, but this is unfortunately lost. We have, nevertheless, an epitome of its contents, for Ralegh asked for a ‘refresher course’ on the eve of his departure for Guiana, which was to take place in February 1595, and Hariot's teaching notes in his own (very crabbed) handwriting, besides fair copies of the tables he drew up, are now at the British Museum.

The ocean weather ship. In 1946 an international conference was held in London as a result of which thirteen ocean weather stations were established. In 1949, for reasons of economy, the number of stations was reduced to ten, and that is the situation at present.

In a previous contribution Professor E. G. R. Taylor has reviewed the development of the sea chart up to 1600, the year in which Edward Wright published his celebrated chart of the world on Mercator's projection. Wright's chart represents one of many minor incursions on the part of English cartographers into the field of nautical cartography, which at that time and for the next hundred years was dominated by the flourishing Dutch school of hydrography. It was not until the latter began to decline towards the end of the seventeenth century that the English cartographer really came into his own and began to produce charts to assist the navigator. Thus the evolution of the English nautical chart to its present state of development covers a relatively short span when measured against the whole background of maritime enterprise and endeavour.

The development over the past two hundred and fifty years has been sporadic rather than continuous, being characterized by sudden advances followed by long intervals of consolidation. Factors such as the needs of national defence, the invention of navigational instruments and advances in hydrographic surveying technique, have at various times acted as stimulants to chart evolution. Throughout the period under review responsibility for supplying the navigator with accurate charts has gradually passed from the many private publishing firms to a specially created national department.

On page 268 of Volume I of this Journal, published in July 1948, A. H. Jessell called attention to a simple method of correcting fixes, or position lines, deduced from astronomical data referred to a fixed epoch, for the effect of precession and nutation since that epoch. This paper has generally been regarded as the first reference to this method, but it now appears that (as so often happens!) it was anticipated by Lieut.-Commander M. Bini, Italian Navy, in ‘Principi di un nuovo metodo per la determinazione immediata del punto nave astronomico’ (On the principle of a new method for the immediate determination of astronomical fixes), a paper presented at the meeting of the Italian Academy of Sciences on 8 November 1947 and later published in Atti della Academia Nazionale dei Lincei (Series VIII, Vol. III, Nov. 1947).

An article by Bini, in which the possibilities of the method were touched upon, was also published in March 1947 in Rivista Marittima.

The writer has compiled a table of altitudes and azimuths for the star Rigil Kent using as argument astrograph times, which are tabulated at four-minute intervals. The tables have been compiled for latitudes S. 35° to S. 39° but could, of course, be extended to all latitudes and for any star. In this note they will be referred to as the Astrograph-time Star Tables.

The Editor welcomes this opportunity of publishing an account of the valuable and fundamental work done by the Navigation Section of the Aeroplane and Armament Experimental Establishment at Boscombe Down. Some of the results have previously appeared in reports with limited circulation, but no full account has yet been published.

The Navigation Section of Aeroplane & Armament Experimental Establishment (A. & A.E.E.) had, at the outbreak of war in 1939, only recently been established, and was in the charge of Squadron Leader (later Air Commodore) D. J. Waghorn, who was followed by Wing Commander W. S. Jenkins. Both of these officers were keenly interested in methods of astronomical navigation, and in development work. Professor H. H. Plaskett, F.R.S., Savilian Professor of Astronomy at Oxford, was attached to the section, and brought to it an invaluable experience in observational theory and techniques.

The work of the section in the earlier part of the war mirrors exactly the state of knowledge in astronomical methods in navigation at that time. A bubble sextant, the Mk. VIII, had been in use for some time, although knowledge of astronomical methods was limited to comparatively few highly trained members of aircrew. The potentialities of astro-navigation were appreciated, however, and the Mk. IX sextant was being developed.

In the list of shore radar installations given as an Appendix to Mr. Le Page's paper (Vol. V, No. 3, p. 295), the installation at Vancouver, B.C., was described as being sited on First Narrows Bridge over the Fraser River. First Narrows Bridge in fact spans the harbour waters between Stanley Park and the North Shore.