for about fourteen days in the Indian ocean, that the water, for want of motion, began to stink; and, that had the calm continued much longer, the stench would probably have poisoned him. It is the motion, therefore, and not the saltness of the sea, that preserves it in its present state of salubrity.[77] The sea has three kinds of motion: the _first_ is that undulation which is occasioned by the wind. This motion is evidently confined to the surface; the bottom, even during the most violent storms, remains perfectly calm. Mr. Boyle has remarked, from the testimony of several divers, that the sea is affected by the winds to the depth only of six feet. It would follow from this, that the height of the waves above the surface does not exceed six feet; and that this holds, in the Mediterranean sea at least, we are informed by the Compte de Marsigli; though he also sometimes observed them, during a very violent tempest, rise two feet higher. The _second_ kind of motion is that continual tendency which the whole water in the sea has towards the west. It is greater near the equator than about the poles; and, indeed, cannot be said to take place at all in the northern hemisphere beyond the tropic. It begins on the west side of America, where it is moderate; hence that part of the ocean has been called _Pacific_. As the waters advance westward, their motion is accelerated; so that, after having traversed the globe, they strike with great violence on the eastern shore of America. Being stopped by that continent, they turn northward, and run with considerable impetuosity in the Gulf of Mexico; from thence they proceed along the coast of North America, till they come to the south side of the great bank of Newfoundland, when they turn off, and run down to the Western Isles. This current is called the _Gulf stream_. It was first accurately described by Dr. Franklin, who remarked also, that the water in it having been originally heated in the torrid zone, cools so gradually in its passage northward, that even the latitude might be found in any part of the stream by means of a thermometer. This motion of the sea westward has never been explained: it seems to have some connection with the trade-winds, and the diurnal revolution of the earth upon its axis.