Page:The American Cyclopædia (1879) Volume II.djvu/87

 ATLANTIC OCEAN 75 The bottom presents here some inequalities in the shape of longitudinal ridges^the effect of which is to press the cold watier of the bottom toward the surface, by which the first indication is produced of those alternate bands of warmer and colder water noticed further north. The warmest water is still found nearer the eastern or right bank of the stream ; but after leaving the straits, and when the stream has gradually widened, the warmest water is on the left or western edge. The stream now runs parallel to the coast, distant from it about 70 or 80 m., turning gradually to the N. E. from the due N. course it had on leav- ing the narrows. It approaches nearest to the land at Cape Hatteras, takes there a slightly more northern direction, and shortly after turns sharply to the east, its rather variable western edge being then about lat. 38. The space between the shore and the stream is occupied by the cold water of the polar current, and the contrast between it and the warm water be- comes more and more abrupt, particularly at some depth, so that the plane of separation received from Lieut. Bache, who first noticed it, the name of the cold wall. At the surface the warm water overflows the cold, forming a thinned-out superficial layer, the limits of which vary somewhat according to the seasons and prevailing winds, certainly much more than the main body of the stream. The bands of cold and warm water increase in number, from three warm ones when coming out of the narrows to six or seven in the section off Sandy Hook ; it must however be remarked that sev- eral of them are very vaguely defined and far from constant. In the same section the depth of the stream is still very considerable, its limits being nearly as well marked by the difference of temperature at 400 fathoms as it is nearer the surface. In the following tables the tem- peratures of the water at different depths are given in a form nearly as plain as in a diagram tor two of the sections. The first is for the section between Cape Florida and the Bernini islands. The full line represents the surface ; above it are given the distances from Cape Florida. The depths are given on the side, and are indicated across the table by dotted lines for every hundred fathoms. The figures of the first line give the temperature from the average of the observations taken at the surface and at 5, 10, 20, and 30 fathoms; of the second line the average at 50, 70, 100, and 150 fathoms ; and in the third are combined the temperatures at 200 and 300 fathoms. The figures arranged vertically over each other represent observa- tions taken at the same station. Table II. is a similar arrangement of the observations in the section off Sandy Hook (New York). The first line gives the temperatures at the same depths as the first line of Table I. ; the second line gives the averages of the observations at 40, 60, 80, and 100 fathoms; the third of the same at 200 and 300 fathoms ; and the fourth the observa- tions at 400 fathoms : TABLE L

100 200 800 10 MILES FROM CAPE FLORIDA. 2O 40 78 74 77 78 78 T9 78 79 70 80 75 44 44 47 43 64 - ( : i, .11. -I depth. TABLE II. FATHOMS.

100 200 300 400 100 M 1 I.I * FROM 200 6ANDY HOOK. 800 400 500 64 50 67 H 65 66 50 52 67 61 66 50 77 60 82 72 79 68 80 68 75 64 78 67 41 48 42 42 48 48 60 68 69 00 60 61 87 40 8S 89 40 40 48 52 56 67 67 66 Both tables show the difference of temperature between the Gulf stream and the inshore cold water or polar current to be distinctly traceable down to 400 fathoms at least ; indeed, in both cases the actual difference is greater near the bottom than at the surface, being in the nar- rows of 10 at 250 fathoms against 7 at the surface, and off Sandy Hook of about 18 at 400 fathoms, while at the surface it is only 14 or 15. The surface differences would of course var.' with the seasons, but it is proper to call attention here to the fact that the stratum of water above 60 is still nearly 300 fathoms thick in this latitude. The theory frequently propounded that the polar current underlies the Gulf stream and penetrates through the