OCEAN OGHAPHY OF THE PACIFIC. 5 



latitude 21° 45' and 22" 8' north and longitude 143° 45' and 143° 20' 

 east three sharp peaks arise along- a line about 35 miles in length 

 and north westerl}^ in direction. On the first, or most southerl}^, the 

 sounding record is 483 fathoms; on the second, about 18 miles awaj, 

 the record is 838 fathoms; and on the third, 20 miles farther to the 

 northwest, 802 fathoms. There are vallej^s 1,000 fathoms deep 

 between these peaks. The indications point to a continuous range of 

 mountains connecting the Ladrone Islands with the Bonin group. 

 After dropping downi the eastern slope of the above-mentioned peaks, 

 the depth increases by an easy gradient to 3,595 fathoms at station 

 1095, rising and falling gently until at station 1126 a sounding of 9Y2 

 fathoms locates an outljdng spur from the Bonin range. Still farther 

 to the northward and westward, at station 1135, the bottom drops 

 to 3,421 fathoms, followed by gentle slopes up to 1,500 and down to 

 2,900 fathoms, until the Gulf of Tokyo is reached. 



GRADIENTS. 



In computing the gradients from station to station serially on the 

 outward voyage onl}^ involving 1,100 soundings, sixty-nine localities 

 only are found where the gradient exceeds 10 per cent. These higher 

 grades are for short distances only, averaging less than 5 miles, and 

 confined to a few regions, especially to the vicinity of Midway Islands, 

 Guam, and the mountain range halfway between the above-mentioned 

 islands. Of the sixty-nine localities showing a grade above 10 per 

 cent, fifty have an incline between 10 and 20 per cent, eleven between 

 20 and 30 per cent, and six between 30 and 40 per cent. At the 

 entrance to Port Tarafofo, on the east coast of Guam, two soundings 

 one-fourth of a mile apart show a difference of depth of 123 fathoms, 

 equivalent to a gradient of about 51 per cent. Also on the declivity of 

 the peak southwest of Midway Islands, which rises to 82 fathoms 

 beneath the surface of the water, there is a change of depth of 1,269 

 fathoms (T,614 feet) in a horizontal distance of 1.8 sea miles, a gradient 

 of 70 per cent. With these few and localized exceptions the bed of the 

 Pacific Ocean, as developed b}^ this surve}^, though rising here and 

 there near to the sea level, and again descending to depths of 5 or 6 

 statute miles, follows easy gradients. On the great plain to the west- 

 ward of the Midway Islands, 1,000 miles in breadth, the average 

 gradient is less than 1 per cent — in one instance only rising to 4.5 per 

 cent, for a distance of 2 miles. 



TEMPERATURES. 



AIR AND SURFACE WATER. 



The temperature of the air on board the ship, and of the water near 

 the surface, was taken at nearlj^ all the sounding stations. These sta- 

 tions numbered, on the average, about ten each day on the outward 



