The need for investigations into the detection of ice by radar became apparent when merchant ships started reporting that ice formations were inconsistent radar targets, and that ships relying upon radar to navigate through ice areas could, in some circumstances, have their safety endangered.

Certain investigations, notably those carried out by the U.S. Coast-guard Service and by the Swedish Defence Research Institute, resulted in the publication of a great deal of useful descriptive information but it was not accompanied by measurements of the actual echoing power of ice targets. With the object of carrying the matter further, a special enquiry was made during the 1950 and 1951 North Atlantic ice seasons, when a number of British ships plying North Atlantic routes completed questionnaires in which the sizes and shapes of ice formations were noted together with their radar detection ranges. This enquiry was instituted by the Operational Research Group in the Marine (Navigational Aids) Division of the British Ministry of Transport, which later analysed the data collected and issued a report. There were, however, certain limitations in this investigation. For example, the performance of the radars was not known, because of their inherent differences and the fact that none of the ships carried instruments, such as echo-boxes, for checking performance; further, propagation conditions at the time of making the observations were not established.

In a previous article in this Journal mention was made of an unexamined manuscript by Hariot belonging to the Petworth Collection entitled The Doctrine of Nauticall Triangles Compendious, which promised to be of interest to navigators. When Lord Leconfield, the owner of the Collection, heard of this he very kindly himself brought this manuscript to the British Museum for study there, and meanwhile Dr. Shirley of the United States, who is at work on other aspects of Hariot's life, sent over from America a transcript from a microfilm copy which was in his possession. The contents of the manuscript more than fulfilled expectation, for it appeared that the main theme was the computation of meridional parts for drawing a Mercator chart and, as Mr. Sadler, the Superintendent of H.M. Nautical Almanac Office, shows in the second part of this paper, Hariot was remarkably in advance of his time in his mathematical treatment of this problem, which continued to be a favourite one for discussion until the discovery of the calculus. As is well known, the first table of meridional parts to be published was that compiled (by simple addition of secants) by Edward Wright (1558–1615) of Caius College, Cambridge, a mathematician who had been nautical adviser to the Earl of Cumberland, and on occasion to the Lord High Admiral himself.

As Professor Taylor has described, the Hariot ms. is largely concerned with the calculation of meridional parts. These calculations are of great interest not only as regards the question of priority, but also because they are based on a method which was more than fifty years in advance of contemporary mathematical knowledge. Although the ms. is paged and cross-referenced, the calculations are incomplete and inadequately explained; arithmetical errors (remarkably few when all calculations had to be done by long multiplication!) make absolute interpretation of all figures almost impossible. Considerable detail is thus unavoidable if the essential parts of the ms. are to be put on record and explained; though the most important point must be left unexplained. There can be little doubt that Hariot's calculations are original and independent.

It is now seven years since the first R.A.F. polar flight was carried out by Aries, a Lancastrian aircraft from the Empire Air Navigation School; during that period air operations in Arctic regions have become an every day occurrence. This paper describes a series of flights undertaken recently by the Royal Air Force Flying College; it is not intended as a discussion of the special techniques of navigation in high latitudes but merely as an illustration of their application in a typical case.

Most navigators will, at some time or another, have noticed the effect of changes in humidity on the dimensions of paper maps or charts pinned up for display purposes. A display chart, or any other large sheet of paper, neatly pinned to a notice board in a warm dry room will tend to sag in an untidy manner if the atmosphere is allowed to become damp. Similarly a chart pinned up in a moist atmosphere is liable to contract and tear away from its anchoring pins if the weather becomes warm and dry. In the same way, the size of a paper chart in use in the air will vary appreciably with changes in atmospheric conditions; and it follows that if the size changes, so does the true scale. Such changes in the scale are of little consequence so long as dividers are used for measuring distances, since it can be assumed that the distance graduations on the chart all expand and contract in proportion to the change in size of the sheet as a whole. But if a graduated rule or straight-edge is used (and this is practicable only in the case of maps or charts based on some projection giving near-constancy of scale) then, quite apart from the scale errors of the projection, changes in the size of the chart will give rise to errors.

This paper will discuss various methods of defining the vertical in aircraft. It is unrealistic to examine the vertical in navigation only in terms of providing a reference for sextant altitude measurement and the paper will therefore discuss more general problems of aircraft stability, which can themselves to some extent be studied by means of the sextant.

The influence of the tides on navigation requires no emphasis to those who have had the responsibility of navigating ships in tidal waters, but there will be few who will have entirely escaped some of the difficulties which tidal problems may bring, especially in unfamiliar waters. Most navigators will therefore have some sympathy for the experience of Alexander and his armies on the way to the mouth of the Indus. Their experience in the Mediterranean had not prepared them for what they had to suffer when they passed into tidal waters.

In all forms of navigation a distinction can be made between the two processes of finding out what the present position is and finding out what direction to go in to reach a given destination. On land the former process becomes the more important of the two because the constraints of natural ground features or of artificial obstacles often make a preset course impossible, as a motor drive along English country lanes shows so well. The destination will often be reached from an entirely unforeseen direction.

The history of Dutch hydrography and chart-making is naturally closely bound up with Dutch sea power and largely follows, or at least followed until recent times, the history of the Netherlands at sea. For four centuries in Holland and for three and a half in the East and West Indies, Dutch surveyors have mapped and charted the coasts, fairways, rocks and reefs. Although in early chart-making a good deal was borrowed from other sources, the contribution of Dutch mapping to safe navigation, has, historically, been extremely important. The Dutch chart of today is a direct development of the traditions set up by the early chart makers.