Soon after the introduction, in March 1947, of GCA to London Airport, it was realized that the advantages which it had brought to approach control could be greatly increased if the range of the radar could be extended to give earlier and more accurate information to the flight information controllers, and eventually the airways controllers, on the position of aircraft. At the time when the Ministry of Civil Aviation had installed and were testing an MEW type radar at the west end of London Airport, the question of the extended cover required from radar in this country was under active consideration. It was thus planned to develop long-range radar control techniques and procedures to be used in conjunction with the MEW radar. The work was planned to fall into three separate stages: (1) experiments in combined MEW/GCA working (termed long-range GCA); (2) operational trials; (3) operational service.

Members will have learned with regret of the death of Dr. L. J. Comrie, M.A., PH.D., F.R.S., who died at the age of 57 on 11 December 1950. Dr. Comrie's contributions to science were primarily in the fields of astronomy and computation, and in the latter field he may be said to have created the modern concept of scientific computing and to have laid the foundations for the present widespread interest in numerical methods and in digital calculating machines. Tributes to this side of his work have already been paid, both here and abroad, and the Royal Society and the Royal Astronomical Society are both publishing fuller notices which will give a detailed assessment of his work. The following note, pays a tribute to Dr. Comrie's contribution to navigation.

The traffic control arrangements of the Royal Aircraft Establishment, Farnborough, although they have never been the subject of intensive operational research, but have been derived by a process of steady growth, may be of interest as an example of what can be achieved by good organization on an ad hoc basis under some of the most difficult operational conditions.

The Royal Aircraft Establishment has an experimental airfield situated in a highly congested area. The London control zone and area is immediately to the north and east, and it is fringed on three sides by civil traffic lanes (Green Airway i in the north and north-west, Red i in the east, and the proposed Red 2 in the south). The Blackbushe circuit of the Ministry of Civil Aviation inter-locks with the Farnborough one in the north north-west, and the circuit of the Odiham R.A.F. airfield, from which jet aircraft are regularly operating, is situated only five miles away in the line of the main bad-weather runway.

A Letter published in the Journal (Vol. IV, No. 2, p. 211) from Captain Brett Hilder refers to the use of the phenomenon known as the green flash for obtaining longitude at sea, and an editorial comment on the letter suggests that accurate descriptions of what has actually been observed at different times at sea might be of value to meteorologists. The following notes, though they contain no reference to using the observations for navigational purposes, may be of some interest as they are the result of a great many observations of the phenomenon.

Numerous reports on observations of the green flash have been published in meteorological publications where, as a general rule, it is accepted that it is only seen under conditions of extreme visibility and clearness of the atmosphere. From numerous personal observations it has been ascertained that this is in fact not so, and that the green flash can be observed under conditions of extreme cloudiness, haze and humidity so long as the horizon is visible at the time of rising or setting of the heavenly body. Another factor affecting the actual sighting of the green flash is the intensity of light emanated by the body, for the flash is of very weak intensity when compared to the normal brilliance of the body observed.

The method of taking high-altitude observations at sea described by A. N. Black in the April number of the Journal is not widely known and is undoubtedly of practical value, though it is not new. In his article Mr. Black regretted that he had had no opportunity of testing the method under practical conditions as his cruising range did not extend into the tropics. For this reason the results of some actual observations taken by the present writer some twenty-five years ago using this method may be of interest to Mr. Black and to readers of the Journal.

The author is in entire agreement with the first ten lines of Mr. Black's paper, though the term slant altitude or inclined altitude might express better what is being measured than horizon distance, which may be misleading. He does not however agree that the method is sound in theory for ‘normal’ altitudes, as will be explained. The method is in fact both practically and theoretically restricted to use with zenith distances of about i°, which is the limit actually considered in Mr. Black's paper.