1872.] 



' Shearwater 3 Scientific Researches. 



595 



directed to prove that the various causes which produced disturbance of 

 equilibrium (among which he enumerates the abstraction of Carbonate of 

 Lime from the Ocean-water by the Coral-forming polypes) are adequate to 

 sustain sensible currents, such as the Gulf-stream. "A constantly acting 

 " power," he says, "such as the force of gravitation, is as necessary to keep 

 " fluids as it is to keep solids in motion. In either case the projectile force 

 " is soon overcome by resistance ; and unless it he renewed, the current in 

 " the sea will cease to flow onward, as surely as a cannon-ball will stop its 



" flight through the air when its force is spent A propelling power, 



" having its seat only in the Gulf of Mexico, or the trade-wind region, 

 " could no more drive a jet of water across the ocean, than any other single 

 " impulse could send any other trajectile that distance through either air 

 " or water. The power that conveys the waters of the Gulf-stream across 

 " the ocean is acting upon them every moment, like gravity upon the 

 " current of the Mississippi river ; with this difference, however, the Mis- 

 " sissippi runs down hill, the Gulf-stream on the dead level of the sea. 

 " But if we appeal to salt and vapour, to heat and cold, and to the secreting 

 " powers of the insects of the sea, we shall fiud just such sources of ever- 

 " lasting changes and just such constantly acting forces as are required to 

 " keep up and sustain, not only the Gulf-stream, but the endless round of 

 " currents in the sea, which run from the equator to the poles, and from 

 " the poles back to the equator ; and these forces are derived from differ- 

 " ence in specific gravity between the flowing and reflowing water. The 

 " w T aters of the Gulf as they go from their fountain have their Specific 

 " Gravity in a state of perpetual alteration in consequence of the change of 

 " Saltness, and in consequence also of the change of Temperature. In these 

 " changes, and not in the Trade-winds, resides the power which makes the 

 " great currents of the sea." (Physical Geography of the Sea, Chapter II.) 



92. The doctrine of Capt. Maury was powerfully and convincingly 

 opposed by Sir John Herschei ; who showed, beyond all reasonable doubt, 

 first, that the Gulf-stream really has its origin in the propulsive force of 

 the Trade-winds, and secondly, that the greatest disturbance of equili- 

 brium which can be supposed to result from the agencies invoked by Capt. 

 Maury would be utterly inadequate to generate and maintain either the 

 Gulf-stream or any other sensible current (Physical Geography, §§ 51-60). 

 But Sir John Herschei did not regard the initial force of the Gulf-stream 

 as adequate to carry it across the Atlantic Ocean, still less to propel it as 

 far as the Arctic Sea ; for he speaks of it as dispersed, and in fact de- 

 stroyed, by the process of thinning-off and superficial extension, about the 

 42nd or 43rd parallel of N. Latitude; and regards the N.E. flow of warm 

 water towards the opening of the Arctic Sea between Spizbergen and 

 Norway as mainly a drift-current swept on by the south-west Anti-trades of 

 extra-tropical latitudes. The Polar current which comes down partly 

 from Baffin's Bay along the Labrador coast, and partly from the east side 

 of Greenland, meeting the Gulf-stream on the Banks of Newfoundland, 



