The quartz clock has made possible a notable improvement in the precision of timekeeping, with the additional advantage of providing a standard of frequency as well. This is perhaps putting the cart before the horse, for the quartz crystal oscillator was developed in the first instance as a precision standard of frequency; it was then adapted, by frequency subdivision and the use of a low frequency output for driving a phonic motor from which seconds impulses could be taken, to serve as a clock. It is primarily from its use as a standard of frequency that it is of navigational interest, for various radio aids to navigation, such as Gee, Loran, Consol and Decca depend upon accurately standardized frequencies. For the satisfactory checking of a frequency, comparison must be made with a standard whose accuracy is at least one degree higher than that of the frequency which has to be checked. Calibration laboratories, in turn, require to check their own standards. As the rotation of the Earth provides our fundamental unit of time, it follows that time, and therefore also frequency, must be determined from astronomical observations; hence it is necessarily the responsibility of the Royal Greenwich Observatory to provide both time and frequency with an accuracy sufficient for all practical requirements. The practical requirements have become more stringent in recent years, and that is why great efforts have been made to improve the precision of time determination and of timekeeping at the Observatory.

The special features of polar navigation are examined with a view to the design of tables for astronomical navigation in polar regions. The use of long intercepts and curved position lines is thoroughly investigated. It is shown that considerable economy of presentation can be achieved; as an example, a one-page table covering all bodies and both polar caps is given. Making the fullest use of polar astronomy, samples are given of permanent tables for the Sun and stars independent of the Air Almana.

The following critical review of tabular methods for astronomical polar navigation was written originally as a comment on a proposal to extend the Astronomical Navigation Tables (at present limited to latitudes between S. 79° and N. 79°) to the poles. Although it has been slightly amended, it has not been entirely recast and it therefore still retains some of the ‘thinking on paper’ of the original version. So far as is known the tables proposed are new, but there is clearly no great originality involved.

In the second issue of the Journal a system of grid navigation was described. This system warrants serious consideration because of its application to polar navigation and because it offers a means of simplifying navigation in high-performance single-seater aircraft of long range. These aircraft are going to present extreme difficulties, particularly in naval aviation, where fixing facilities and pilotage are limited.

Prior to the outbreak of war in 1939, flight planning procedure was not generally practised in civil aviation operations except in a few outstanding cases. Such operations as the Imperial Airways transatlantic flying boat flights called for the careful compilation of a flight plan in order that an indication of the flight time could be obtained. Since the range of these boats did not provide for any very great reserve, the flight plan was obviously an essential part of the preparation for the flight. In the case of a few shorter range operations, flight planning was also carried out to a certain extent: one operator, for instance, adopted a procedure whereby departures and arrivals were made to a schedule, and the aircraft operated so as to comply with this schedule. The increase in the length of route stages and the need for more technical operation of aircraft from the economic point of view indicated the need for more general use of serious flight planning, and it is now well established that flight planning is essential to the safe and efficient operation of flights of all kinds.

The method described provides glide-paths for climbing and descending aircraft by combining in a single instrument information from the barometric altimeter and radar distance measuring equipment. Preliminary flight tests have shown that the method provides a smooth path along which an aircraft can be flown within close limits, and is one that appears sufficiently promising to justify further development.

Height separation has for years been a fundamental concept in the control of air traffic. It is the basic method of preventing collision during en-route navigation and in some holding procedures. The main reason for this is that a suitable instrument already exists in the form of the barometric altimeter, aninstrument which is intrinsically more accurate and reliable than any of the usual navigational aids.

When designing the periscopic sextant now coming into production it was realized that the conditions in the pressurized aircraft for which this sextant was designed differed sufficiently from those previously experienced to make it worth while reconsidering what methods would be most applicable to the new combination of pressurized aircraft and periscopic sextant.

The conditions differ from previous experience in providing (a) a higher speed; (b) very little, if any, direct view of the sky by the navigator.

Static electrical charges from the atmosphere can in certain circumstances become attached to an aircraft in flight. This can prove dangerous to flight if radio aids to navigation are being relied on as the electrical charges result in precipitation static interference. The phenomenon was at first confused with the interference to radio resulting from transient atmospherics, although precipitation static interference is in fact largely of a continuous nature.

At the request of the Ministry of Transport and the Humber Conservancy Board, a visit was made to the River Humber in H.M.S. Fleetwood to determine whether the navigational marks at present in use would be suitable for pilotage of the river in poor visibility by a ship fitted with a U.K. radar.

In present designs of radar sets for merchant ships, the radar-equipped ship is represented as being at the centre of its own P.P.I. picture. But there is a case for having an off-centre display. In this article are discussed possible advantages to be obtained from such a display, when the set is being used for collision warning away from a coast-line. The author recognizes that some of the opinions expressed are of a controversial nature.

The calculation and publication of the errors in measured altitudes due to tilt of the sextant serve a useful purpose in impressing users more strongly with the need for care than does the unbacked advice to rock the sextant always given in the text-books, and also in indicating that carelessness carries greater penalties the greater the altitude. The work once done is done for ever, so we may as well get the sum right.