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

APPENDIX. 287 Java ; on that of Sumatra ; at Ceylon ; at the Laccadiva Islands at the Seychelles ; on the coast of Madagascar ; and at Amsterdam Island, at twelve : but at the Chagos Islands and Mauritius it is high water at about nine, and at the Keeling Isles about eleven. Here, then, it would seem that there is cause for much perplexity. Having now stated the principal facts which occur to my mind, I will mention the conclusions drawn from them, and then attempt to explain the anomalies. Let E G (fig. 1.) represent a section of our globe, of which A B C D is supposed to be land, and E F G H water. Let H M show the direction in which the moon's attraction would operate. The effect of her attraction, according to Newton's demonstration, would be to raise the water at F by positive attraction of the water, and at H by attracting the earth more than the water : — let the dotted line represent the consequent figure of the ocean. In fig. 2, let the ocean be supposed 90° or six hours wide ; let the moon act in the direction M F ; and let the dotted line represent the altered position of the water when moved out of its natural position (with respect to the earth) by the moon's attraction. Again, in fig. 3, suppose the moon acting in the line M K, and the dotted line representing the figure taken in that case by the ocean. It will occur to the reader that but little water can rise at F and H (fig. 1), at F (fig. 2), or at K (fig. 3), unless water falls or sinks, at E and G (fig. 1), G (fig. 2), F and G (fig. 3). because water is but slightly compressible, except under extraordinary pressure, and because it is incapable of being stretched ; therefore, if at any place the sea is raised above its natural level, the excess must be supplied by a sinking taking place elsewhere. There cannot be a void space left under the sea between the water and its bed ; and there is no lateral movement of the particles at the surface only of the ocean sufficient to cause high tides on either shore : therefore the conclusion may be drawTi, that the whole mass librates or oscillates. By librating I mean such a movement as that which a large jelly would have, if its upper part were pushed on one side,, and then allo-wed to vibrate while the base remained fixed : and by oscillating I mean a movement like that of water in a basin, after the basin is gently tilted and let down again : and that such a motion would be