Captain A. Wepster's able and professional analysis of this subject, contained in the January issue of the Journal, confirms what many seamen have long known. That these rivers—the Schelde, the New Waterweg, the Weser and, finally, the teeming Elbe, from Brunsbuttel seaward—are the world's most difficult and demanding stretches of navigation for seamen and pilots. The Captain's excellent treatment focuses attention on this and in his final paragraph he offers several considerations which, if followed, could reduce the number of collisions.

I refer to page 29; ‘Improving River and Port Authority Organizations and, if necessary, traffic control. On page 17, with reference to changing pilots in Flushing Roads in the Schelde; who has not, when proceeding outbound, ‘overshot’ the mark when approaching the pilot ground off the Commercial Harbour ? There follows the business of making a complete circle midst moving traffic as an apologetic pilot comes a puffing to the bridge, showering abuse on the man he relieved because 'he failed to slow down in time’.

I would add a specific recommendation to those offered by Captain Wepster: For vessels outbound from the Schelde, to disembark their pilots and take on Oostgat or Wandelaar pilots at a point approximately three miles upriver, say at Sloehaven. A pilot station could be maintained at that point in the manner of the present pilot office at the Flushing Mole.

In the Working Group Report (19, 411) a mistake in the figure quoted (page 415 , paragraph 5) for the number of collisions analysed in Appendix I (2648 not 2748) results in minor corrections to a number of the figures quoted in the first two pages of Appendix I. These in no way affect the arguments put forward. On page 415 of the Journal (page 5 of the separately published version) paragraph 5 , lines 1 and 2, should now read:

‘An analysis of some 2648 collisions selected randomly (Appendix I) showed that 70 per cent occurred in port areas and 30 per cent at sea.’

The amendments and additions to the existing (1960) Regulations for Preventing Collisions at Sea which were offered in the Journal, 20, 103, by Captain Burger and Captain Corbet have been studied with interest. While clearly we have the same objectives at heart it will be seen from the comments that follow that the proposals are virtually unacceptable.

Rule 16 (b)

It is felt that the proposed re-wording is inappropriate as the words ‘hearing, apparently forward of her beam’ and ‘the position of which is not fully ascertained by sighting’ do not make sense in one sentence. Moreover, the proposed addition of the word ‘particular’ before ‘caution’ is not likely to deter the delinquent any further than the original wording.

It is agreed that the present wording of Rule 16 (b) may leave something to be desired in the interpretation which can be put on ‘ascertainment of position’; this has in fact been evident by some of the different interpretations which have been given by the Courts.

In the Nippon Yusen Kaisha v. China Navigation Co. case of the pre-war era (1935), Lord MacMillan said, ‘In order that the position of a vessel may be ascertained by another vessel within the meaning of the Regulation she must be known by that other vessel to be in such a position that both vessels can safely proceed without risk of collision’.

Recently the author was asked to suggest how an old (Scottish?) sun-dial, inscribed on a slate slab about 50 cm across and 3 cm thick, could be put into working order and set up correctly to tell the time. Upon examination the dial was found to be of considerable historic interest. Although it was quite a well-known type of dial—an equatorial—the furniture and inscriptions suggested a definite connection with the sea. Moreover, no other identical instrument is known to exist; possibly the publication of this note may help to bring other specimens to light. For this reason it is felt that a description of the various features of this multi-purpose dial will be of some interest.

Both surfaces of the dial are shown in the accompanying photographs. For clarity, a fine talcum powder was sprinkled on the dial to fill all the incised markings which would otherwise be invisible. Unfortunately the gnomon is missing. This gnomon would have passed vertically through the dial extending on either side for not less than 10 cm. Probably two circular discs with pointers were mounted centrally on the upper surface, with one of these discs bearing an arm with the ‘dioptera’, but unfortunately these items are also missing. The discs would have been capable of rotating around the gnomon. It would appear that some modifications became necessary after its construction as the four holes around the inner circle have spoilt the lettering.

In the October issue of the Journal (19, 529), Commander Clissold puts forward a type of radar display which might be useful for collision avoidance, as it intends to show the aspect of the ship representing the danger. To achieve this a long afterglow screen would be used and the display would be oriented head-up, i.e. ship's head at the top of the picture to correspond as closely as possible with a possible visible situation. An electronic cursor, bearing line, would indicate a danger of collision if on constant bearing. This type of display is said to show tracks true relative to own ship's course.

Apart from the fact that 30 seconds afterglow, decaying exponentially as an excited phosphor screen would, might be too short for showing up tracks efficiently, there are some other difficulties as well with such a display. Obviously aspects of target ship would not be shown but implied only by the afterglow track. Furthermore, a display of this kind would be a true-motion type display not necessarily north stabilized but nevertheless showing all motion of other ships in true, if own ship's speed is compensated for in displacing the origin of the radial scan. The difficulty will arise if own ship changes heading and unless this heading change is also compensated for, like in a north-up stabilized true-motion display, smearing of all echoes will occur. A heading change of own ship, therefore, will produce additional apparent tracks of other ships and the apparent displacement of fixed targets.

In an article in this Journal some years ago, the late Professor E. G. R. Taylor and Dr. D. H. Sadler drew attention to and discussed Hariot's calculation of meridonal parts. The question was raised but not answered as to ‘how Hariot discovered the extremely complex and far from obvious method’ that he used. This note draws attention to a possible, and indeed a very likely, way in which the method may have been discovered.

The conformal property of the stereographic projection of the surface of a globe from a pole on to its equatorial plane has been known since antiquity. It is used in the design of the astronomer's astrolabe. Hariot's manuscripts contain in more than one place a diagram for a proof of the property. One of these is reproduced in a recent article on Hariot. Halley, in an article on meridional parts, says of the conformal property, ‘But this not being vulgarly known, must not be assumed without a Demonstration’. From this result he obtains the formula for meridional parts, unaware that the same proof may have been used almost exactly a hundred years previously. In fact, he says, ‘I hope I may be entituled to a share in the emprovements of this useful part of Geometry’ on the basis of ‘having attained … a very facile and natural demonstration of the said Analogy’.