TIDE-RIPS AND SEA DRIET. 381 



it is above that due the latitude. Therefore, in a mere diagram, 

 as this plate is, the numerous eddies and local currents which are 

 found at sea are disregarded. Of all the currents in the sea, the 

 Gulf Stream is the best defined ; its limits, especially those of the 

 left bank, are always well marked, and, as a rule, those of the 

 right bank, as high as the parallel of the thirty-rifth degree of 

 latitude, are quite distinct, being often visible to the eye. The 

 Gulf Stream shifts its channel (§ 124), but nevertheless its banks 

 are often very distinct. Ships, in crossing the edges of it, can 

 sometimes know it by the colour of the water ; at other times they 

 find, as they pass along, the temperature of the Avater to change 

 8° or 10^ in the course of as many minutes ; as an example of 

 this, I quote from the abstract log of the " Herculean," in which 

 Captain William M. Chamberlain, being in latitude 33° 39' north, 

 longitude 74° 56' west (about one hundred and thirty miles east 

 of Cape Fear), remarks ; " Moderate breezes, smooth sea, and fine 

 weather. At ten o'clock fifty minutes, entered into the southern 

 (right) edge of the Stream, and in eight minutes the water rose 

 six degrees ; the edge of the stream was visible, as far as the eye 

 could see, by the great rippling and large quantities of Gulf weed 

 — more ' weed ' than I ever saw before, and I have been many 

 times along this route in the last twenty years." In this diagram, 

 therefore, I have thought it useless to attempt a delineation of 

 any of those currents, as the Rennell Current of the North At- 

 lantic, the " connecting current " of the South, " Mentor's Counter 

 Drift," " Rossel's Drift of the South Pacific," etc., which run now 

 this way, now that, and which are frequently not felt by naviga- 

 tors at all. In overhauling the log-books for data for this chart, 

 I have followed vessels with the water thermometer to and fro 

 across the seas, and taken the registrations of it exclusively for 

 my guide, without regard to the reported set of the currents. 

 When, in any latitude, the temperature of the water has ap- 

 peared too high or too low for the latitude, the inference has been 

 that such water was warmed or cooled, as the case may be, in 

 other latitudes, and that it has been conveyed to the place where 

 found through the great channels of oceanic circulation. If too 

 w^arm, it is supposed that it had its temperature raised in warmer 

 latitudes, and therefore the channel in which it is found leads 

 from the equatorial regions. On the other hand, if the water be 

 too cool for the latitude, then the inference is that it has lost its 

 heat in colder climates, and therefore is found in channels which 



