Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2- Appendix): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

284 APPENDIX. In the greatest expanse of ocean, that which meets with only par- tial interruption to free tidal movements — the zone, if it maj"- be so called, near fifty-five degrees of south latitude — there Is high water at opposite sides, and low water at opposite sides of the globe nearl}'^ at the same time. At the eastern part of the Falkland Islands, exposed to the tide of this zone, it is high water, or full sea, at about nine o'clock on the day of new, or full moon, by Greenwich time ;* and on the southern shore of Van Diemen's Land it is high-water at about ten. This is not a point exactly opposite, it is true, but it is the nearest so at which we have yet observed. At each of tliese places the tide rises six hours and falls six hours, alternately ; therefore when it is low water at one, it is also low water at the other. There is no intermediate place in this zone, rather distant from these points, at which I know of a tide observation deserving confidence ; but those above-mentioned are certain, and corroborate the Newtonian theory in a satisfactory manner. This is, however, the only zone of ocean, which is at all able to follow the law which would govern its undulations if the globe were covered with water. In other zones (taking about ten degrees in latitude as a zone) it is high water, generally speaking, at one side of an ocean near the time that it is low on the other. In oceans about ninety degrees wide, this happens very nearly but as the width diminishes, so do the times of high water at each side approach ; and as the viidth increases beyond ninetj' degrees, as in the case of zones of the Pacific, the times of high water still approach (in consequence of the tendency to high M'ater at opposite points), and farther confirm the Newtonian theory. For examples (on the day of full moon) : — In the Pacific, at Port Henry, in 50° S. it is high water at 5h. at M'hich time it is near low water at Auckland Island, where the time of high tide is 12h. 30m. In this case, the interval between one high water, and the other on the opposite side of the ocean, is 7h. 30m. or 4.30 ; and the ^vidth of that ocean is nearly eight hours (measured in time.) At Valdivia, in lat. 4C° S. it is high water at 3h. 30m. and at New Zealand, on that parallel, at 9h. 50m. The space of ocean between is seven hours nearly : the diflTerences are 6.20 and 5.40. * Towhicli all tlio tinips are iiere reduced for easy comparison.