WAVES OF THE SEA. It may easily be observed that when smooth water is struck by wind the surface is imme diately covered by a ribbed pattern of transverse inequalities about one inch from crest to crest travelling very slowly in the direction of the wind, and however long the breeze con tinue there is no increase of their size or speed immediately adjacent to the shore off which it blows. To leeward, however, there is an increase in the height and speed of the ridges and the distance between their crests. This distance is called the wave-length, the distance for which an individual ridge can be traced, the crest-length. In the deep waters of the open ocean the height, speed and wave-length is limited only by the velocity of the wind, but even the largest lakes have not sufficient room for full growth. Our knowledge of the height of waves at sea is mostly obtained by the primitive method of finding how high above the ship's water-line the observer must stand so that the passing crests shall top the horizon.
During a voyage from Liverpool to Boston, U.S.A., by the "Ivernia" the wind on Dec. 7, 190o, was a strong gale, number 9 on Beaufort's scale of force, reckoned as having an average speed of so statute or land miles per hour. The writer observed that the waves, which met the ship at a considerable angle, usually topped the horizon when the view-point was 3o feet above the ship's water line and that a position 43 feet above that line had to be taken up in order to be on a level with the tops of the largest waves.
On Feb. 9, 1907, bound from New York for Southampton there was only a moderate breeze, but the "Minnehaha" rolled heavily in a huge swell from the north-west. The origin of the swell was revealed to us by a message from the "Cedric" to the north, which reported a strong north-west gale. The actual level of the trough of the waves was determined by means of a heavy rope let down over the ship's side, and the true height of the swells, which were of nearly uniform size, was found to be slightly more than 41 feet. Of the height of waves in a whole gale, Beaufort's force so, average wind velocity 59 miles per hour, the writer has obtained estimates from master mariners, with the details of accompanying conditions which are necessary to give precise meaning to these statements. The records prove a height of nearly so feet.
Formula and Practice.—On Dec. 29, 1922, in the course of a prolonged storm in the North Atlantic, the wind reached and maintained for a considerable time the maximum or hurricane velocity, computed at 75 miles an hour and upwards. The "Ma
jestic," hove-to and rode easily among the waves which were of remarkable regularity and phenomenal size. Under these favour able conditions observations were recorded and it was found that the height of the waves from trough to crest exceeded 7o feet It is clear that the height of the waves finally produced in the open ocean is in direct, simple proportion to the velocity of the wind. The larger waves occurring at short intervals which chiefly attract attention have about eight feet of height, reckon ing from trough to crest, for each 1 o miles-an-hour velocity of wind, but their apparent height is less when the ship is borne upon two waves.
In order to determine the height of the waves we must place ourselves so as to be on a level with the crests. In judging from this level the wave-length or distance between crests, dimensions have been obtained far below that which had been calculated by the usual mathematical formula from the period of the waves, the interval of time between the arrival of crests, and the ques tion therefore arose whether the eye had been deceived or the calculation applied to conditions not contemplated in the mathe matical theory. The answer was obtained by the writer on Dec. 21, 1911, when the "Egypt" was hove-to in the Bay of Biscay. The waves rose rather more than 3o feet above the ship's water-line, and from the promenade deck, which gave an eye height of 27 feet, the wave-length appeared to be scarcely equal to the length of the vessel whereas the period indicated that it should be greater. Ascending to the navigating bridge where the view-point was 54 feet above water-line the whole length of the ship was seen to lie well within the interval between wave-crests, and the wave-length as judged from this position agreed with the period. The apparent wave-length from this elevated position was also in mathematical agreement with the speed of the waves which was determined from the time which they took to run the length of the stationary ship. That the eye is so greatly deceived in judging wave-length from near the level of the crests is due to the very slight convexity of the ridges, and the apparent brow of both the receding and advancing wave being much nearer than the true summit.