Page:A Voyage to Terra Australis Volume 1.djvu/297

King George's Sound.]

This is what I allowed in tracing a base line upon the beach between the two harbours; and the back bearings from different stations did not vary more than a degree from it; except at the west end of Michaelmas Island, where the variation, in one spot, was greater by 3°.

The above different variations show that the needle was affected by the rocks; and there will be frequent occasion, in the course of the voyage, to point out similar anomalies in the observations on land; for they were found to take place upon almost all those parts of Terra Australis, where the basis stone is of granite, as here; and also in those where green-stone, porphyry, basaltes, or iron-stone prevail; whereas in the lime, or grit-stone countries, the needle did not appear to suffer any derangement. In the Appendix No. II. to the second volume, where the changes on ship board, which arose from altering the direction of the head, are explained, this subject of the differences on shore is mentioned; for they also were not without a certain degree of regularity.

No set of Tide was perceived on board, either whilst the ship was in the Sound, or in Princess-Royal Harbour; nevertheless it was sometimes found to run with considerable strength in the narrow entrances of both harbours. According to lieutenant Flinders' observations on shore, during sixteen days, there was only one high water in twenty-four hours; which always took place between six and twelve at night: for after, by gradually becoming later, it had been high water at twelve, the next night it took place soon after six o'clock; and then happened later by three quarters of an hour each night, as before. The greatest rise observed was three feet two inches, and the least two feet eight inches. The accumulation was made in this manner: After low water, it rose for several hours; then ceased, and became stationary, or perhaps fell back a little. In a few hours, it began to rise again; and in about twelve from the first commencement, was high water. It was observed by captain Cook upon the east coast of this country, and since by many others,