364 EXPEDITION TO JAFAN. 



sent the days of the month. Next below the "daily winds" is a barometric scale, divided off 

 into equal parts, for days by the vertical lines, and into tenths by the horizontal lines, the last 

 of which are marked at the side of the diagram. 



This scale is traversed by a broken line, which indicates, at its intersection of the vertical 

 lines, the mean diurnal atmospheric pressure. 



The next is a thermometric scale, divided off in the same manner as the barometric scale, but 

 graduated at the side for degrees, instead of tenths, and traversed by a red line, to indicate, at 

 its intersection of the vertical lines, the mean daily temperature of the air ; and by a blue line, 

 to indicate, in the same manner, the mean daily temperature of the water 



These daily means, of both the barometer and thermometer, were obtained from observations 

 taken at the hours of 3 a. m., 9 A. m. ; noon, 3 p. m., 9 p. m., and midnight. 



In the narrow space intervening between the barometric and thermometric scales are the 

 days of the month, embraced in the passage of the ship from port to port, and corresponding to 

 the vertical lines by wbich those scales are intersected. 



On the lower part of all the plates (except Nos. VIII and X) is a sectional chart, with the 

 latitudes marked at the side, and the longitudes at the bottom 



On this chart is traced the track of the ship, with her position every day at noon ; the direc- 

 tion of the daily current, as obtained from the reckoning, denoted by small arrows, and its 

 amount per day in nautic miles, expressed by numerals at the points of those arrows. 



I have not multiplied the diagrams further than what I considered absolutely necessary to 

 convey a general, yet accurate, idea of the direction, velocity, and limits of this remarkable 

 stream. You will find it traced upon the accompanying chart, being represented by the shaded 

 space lying along the western shores of the North Pacfic. 



The existence of a northeast current on the coast of Japan, was noticed by Cook, Kruzen- 

 stern, and other explorers, and has, of course, not escaped the attention of more recent intel- 

 ligent navigators,* but I believe no systematic series of observations upon it have hitherto been 

 made. 



The Japanese are well aware of its existence, and have given it the name of " Kuro-Siwo," 

 or Black stream, which is undoubtedly derived from the deep-blue color of its water, when 

 compared with that of the adjacent ocean. 



The fountain from which this stream springs is the great equatorial current of the Pacific, 

 which, in magnitude, is in proportion to the vast extent of that ocean when compared with the 

 Atlantic. 



Extending from the Tropic of Cancer, on the north, to Capricorn — in all probability — -on the 

 south ; it has a width of near three thousand miles, and with a velocity of from twenty to sixty 

 miles per day, it sweeps to the westward in uninterrupted grandeur, around three-eighths of the 

 circumference of the globe, until diverted by the continent of Asia, and split into innumerable 

 streams by the Polynesian Islands ; it spreads the genial influence of its warmth over regions 

 of the earth, some of which — now teaming in prolific abundance — would otherwise be but 

 barren wastes. 



M. Biot, in his description of the general system of currents in the Pacific, says: "A third, [branch of the equatorial 

 current,] rejected by the eastern coast of China, turns to the northward. But this soon meets, directly in its course, with 

 the Japanese archipelago, the Peninsula of Kamtschatka, and the eastern prolongation of Siberia. Besides this it is driven 

 towards the equator by the Polar current, which issues from Behring's Straits. Under the combined influence of these 

 causes, its course bends to the eastward, and following the direction, now quite open to its progress, it proceeds to the 

 western shores of North America, above the Oregon Territory," &c. 



