The CHAIRMAN moved a vote of thanks to the Author for his Paper.The Author.The AUTHOR suggested two points in particular which he thought might be discussed with advantage. It would be interesting to have, first, an opinion, from the nautical standpoint, of the value of harbours of refuge projected into the open sea, and unsheltered from the wind by high lands abutting upon them; and, secondly, an authoritative opinion as to the area of water which ought to be provided for vessels of the maximum draught-battleships, for instance-riding at anchor in partly-sheltered waters.
Mr. Mnttheas. Mr. WM. MATTHEWS (of Westminsterj pointed out that Figs. 3-20represented theoretically what might be expected to occur under the conditions indicated in the Paper. I n looking a t such questions i t was important to take into account the particular physical conditions of each case. For instance, wave-force was the most effective influence in the movement of sand on beaches and in the vicinity of works ; and a t Dover, where the works had been going on for several years, the highest recorded wave measured about 15 feet from crest to trough. There might some day be an abnormal wave ; but hitherto no wave of greater height than that had been met with. On the Tyne, however, where the work in connection with the North Pier had been in progress for about 5 years, the resident engineer had reported that he had measured waves of 35 feet and 40 feet from crest to trough ; and Mr.Wm. Shield (of Westminster), had measured similar waves a t Peterhead. The difference of the wave-force in those cases must materially influence the accumulations of sand in the vicinity of the works, and also the general configuration of the sandbanks under water.With regard to the currents and range of tide, a.t Colombo, where there was a considerable quantity of sand south of the harbour, the range of the spring-tide was 2 feet, and, as might be expected, there was very little current action. At Dover the range of tide was 18 feet 9 inches, and it was necessary to contend with currents of 4 knots per hour. With practically no current in the one case, and a current of 4 knots per hour in the other, there must be a considerable difference in the action of waves in the vicinity of the respective works. Striking instances of the effect of the Downloaded by [] on [12/09/16].