736 
THE VOYAGE OF H.M.S. CHALLENGER. 
The temperature of the water at the bottom in this section was generally the same 
as that at 1400 fathoms, viz., 35° '3, from which it appears probable that this portion of 
the Pacific Ocean is cut off from the general circulation by a ridge joining Japan with 
the Admiralty group through the chain of small islands stretching in an almost continuous 
line from Japan through the Bonin, Ladrone, and Caroline Islands to the Equator. 
The surface temperature, which at the Admiralty Islands was 8 3° '7, continued above 
80° for nearly 1000 miles, and even as far north as the 22nd parallel was over 78°. 
Between the 22nd and 25th parallel it fell 8°, and continued at an average of 6 9° ‘5 
to the 30th parallel, after which it varied between 56° and 68° to the coast of Japan, 
being 55° in Yokohama Bay. 
The serial temperatures showed that from the Admiralty Islands to the 14th parallel 
of north latitude, a mass of warm water above the temperature of 80° extended from the 
surface to the depth of from 50 to 90 fathoms. Below this warm surface stratum the 
temperature decreased very rapidly (on one occasion altering 15° in 11 fathoms), until 
at 300 fathoms it appeared to be very nearly constant at 45°. The isotherm of 45° 
remained at the depth of 300 fathoms from the Admiralty Islands to the 15th parallel, 
northward of which it sank to 400 fathoms. Between the 15th and 26th parallels the 
isotherm of 40° was constant at 500 fathoms ; northward of the 26th parallel it rose 
towards the surface, as did also the isotherm of 45° (see Diagram 16). The isotherm of 
45° was also at the depth of 300 fathoms in the Banda, Celebes, and China Seas ; and 
the isotherm of 40° was found at a depth of 500 fathoms in the China Sea in January. 
Anemometer observations were taken daily during the passage, from which it appeared 
that between the 1st and 6tli parallels of north latitude, the mean velocity of the trade 
wind was only 6 miles per hour. North of the 6th parallel the velocity gradually increased, 
until in 10° N. it was 22 miles per hour, which was the maximum attained ; it then 
gradually decreased to 8 miles per hour in 17° N., and from that parallel to 20° N. only 
averaged 5 miles per hour. After losing the trade, the velocity of the wind varied 
considerably, but it never exceeded a rate of 22 miles per hour. 
No current observations were taken except the surface set, which was ascertained by 
frequent astronomical observations. 
In April, when nearing Japan, the temperature of the surface water fell from 70° 
to 64° between 6 p.m. on the 8th and 1 a.m. on the 9th, so the ship having apparently 
entered the Japan Stream, a sounding was taken at 5.30 a.m. in 2250 fathoms, but little 
or no current was observed, the position at this time being lat. 31° 8 7 N., long. 137° 8' E. 
After completing the sounding the vessel proceeded to the northward, the surface 
temperature varying from 63° to 64^° until 6 a.m. on the 10th April, when in lat. 
32° 35' N., long. 137° 45' E., it rose suddenly to 68°. At noon the ship’s position was 
lat. 32° 55' N., long. 138° 25 ' E., and a current of 42 miles N. 22° E. (true) had been 
experienced since noon on the 9th. This position was fixed by meridian altitude, and 
