Hitherto the altitude of a wave has been generally measured merely by the eye, so that the result depended too much on the accuracy of individual observation to admit of its being exactly ascertained; and it is for this reason that the statements relative to the maximum height of the ocean wave are so various that they cannot be considered reliable, for whilst some observers estimate them to be from 60 to 70 feet, others reckon them only at from 30 to 40 feet.
On board the Novara the following method of admeasurement was adopted: we first determined, by a chronometer, the time that a wave takes to pass from one end of the ship to the other, whereby the velocity of the progressive motion of the wave could be calculated in relation to the ship's course and speed, regard being had to the direction and velocity of the ship against it. With this velocity ascertained, we were in a position to determine and fix the average distance between two consecutive waves. Lastly, the height of the wave was ascertained from the angle at which the frigate rose and fell in the line of its keel, by the influence of each successive wave and by means of the ascertained distance from the trough of the sea to the crest of the wave. Though this method, likewise, has many difficulties and deficiencies, yet it appears well suited to make correct comparisons between the different waves; and, under certain favourable conditions, it yields so accurate a result, that at any rate it is to be preferred to mere guess-work, besides that the experiment itself is susceptible of many improvements. It seems safe to assume that waves scarcely ever attain an elevation of more than 40 or 45 feet.
The gale had driven us a long distance out, and only after great trouble did we again near the land. On the 1st of October the Cape came once more in sight; we tacked, in order to get into the wide gulf termed False Bay, by which in some respects the peninsula of the Cape is formed, being separated only by a low sandy plain from the Atlantic. Whittle's rock renders tacking in its neighbourhood in so far more difficult, as the existing charts of the bay are not sufficiently exact to be implicitly relied on. Buoys have often been fixed in that quarter, but every new gale carried them away again; so that the position of the rock is not indicated. An English pilot now came on board, who brought papers, and intelligence that a number of letters were waiting for us. Our impatience became stronger when towards evening the light breeze entirely ceased, and we thereby were forced to bring up at a distance of a mile and a half from the actual anchorage. About the same time an officer arrived from the British line-of-battle-ship Boscawen, under the flag of Rear-Admiral Grey, in order to serve as a guide should no pilot have boarded us.
On the 2nd of October, at 7 a. m., the anchor was let go in Simon's Bay, a spacious but gloomy-looking sheet of water. Here ships ride much more secure than in Table Bay, from which, in a stiff westerly or north-westerly breeze, vessels are often forced to run out to sea to avoid being driven on shore. The communication with the land is thus sometimes interrupted for days. From Simon's Bay to Table Bay, round the Cape the distance is forty miles, whilst by land the journey to the capital of the colony is, with good horses, performed in three hours.
CABO TORMENTOSO.