298 OBSEEYATIONS ON THE CUEEENTS. 



sea exploring expeditions, samples of water have been brought up from 

 the greatest and intermediate depths, and on analysis the components 

 have been found to be in all cases almost identical, the exception being 

 that at great depths the proportion of lime is larger. Animal life, also, is 

 found ai great depths, adapted to the great pressure under which it exists. 

 Dtiring the voyage of H.M.S. Bulldog, in the summer of 1860, when nearly 

 midway between Ireland and Greenland, there were brought up from a 

 depth of 1,260 fathoms, or nearly 1| statute mile, several live starfish, which 

 had clasped their slender arms round that part of the sounding line which 

 lay on the bottom. Now, as the process of winding this line in would 

 occupy upwards of an hour, had the water varied in character even in a 

 slight degree, they would have loosened their hold and died. 



It is needless to pursue this subject further now. It will be found more 

 amplified hereafter, when the question of the Depth of the Atlantic is dis- 

 cussed. It is only here cited in order that should the mariner in the course 

 of his voyage be able, from his own observations, to add to our knowledge 

 of this subject, it will afford him gi-eat interest, and be beneficial to the 

 rest of the world. 



(247.) The subject of the Temperature of the Ocean will also be treated 

 of specially hereafter. It is of importance in some localities, as it will 

 indicate the changing from one Current to another, as from the Gulf Stream 

 into the cold Arctic Current within it, or the reverse. It was formerly 

 thought that a decrease of temperature was a sure indication of approach- 

 ing shoal water, and its study was therefore inculcated as a precautionary- 

 measure. This point, however, has been shown to be in general fallacious. 

 It arose from the fact that vessels crossing the Gulf Stream, or attaining 

 soundings on the American coast, experienced a very sudden decrease of 

 heat in the water. This is now accounted for in a very different way; 

 therefore this topic is not of so much importance in the practice of navi- 

 gation as it was formerly thought to be. 



(248.) Leaving for future Sections (those on the Gulf Stream, and on the 

 Depth, Temperature, and Circulation of the Ocean) the remarks on the 

 origin and causes of Ocean Currents, it may be here briefly remarked that 

 the action of the Wind seems to be a main cause of the general surface 

 circulation. Doubtless there are several other forces which combine with 

 or help to neutralize the action of the Wind, such as the Tidal Wave, the 

 rotation of the earth, the differing effects of Temperature, of Specific 

 Gravity on the surface, and of the very difticult subject of wave-action, 

 which should be taken into consideration. But the tiny ripple raised by a 

 breath of air on the surface of still water, enlarged by accumulation into 

 an oscillating wave by a more powerful wind, may be driven forward into 

 a wave of translation, and thus the Wind becomes the real origin of a 

 Drift and finally a Stream Current, which may be satisfactorily traced over 

 a great portion of the Ocean surface. 



(249.) There are many evidences that the general surface Currents, 

 which alone control a ship's movements, have but very little depth. A very 

 few fathoms below the surface their velocity and power become much 

 decreased, and it is more than probable that at a moderate depth, com- 

 pared with the dimensions which have been usually attributed to them, 



