CHAP. I. ] THE EQUIPMENT OF THE SHIP. 85 
Sea, is the extent to which the colder and therefore heavier water may 
run up-hill on the sides of declivities. The position of the Azores will 
probably be found very suitable for observations of this kind. Tem- 
perature-soundings should be taken at various depths, especially on 
their north and south slopes, and in the channels between the islands ; 
and the temperatures at various depths should be compared with those 
of corresponding depths in the open ocean. 
It is in the southern oceans that the study of ocean-temperatures at 
different depths is expected to afford the most important results; and it 
should there be systematically prosecuted. The great ice-barrier should 
be approached as nearly as may be deemed suitable, in a meridian nearly 
corresponding to the centre of one of the three great southern oceans— 
say to the south of Kerguelen’s Land; and a line of soundings should 
be carried north and south as nearly as may be. 
In connection with the limitation of the area and depth of the reef- 
building corals, it will be very important to ascertain the rate of reduc- 
tion of temperature from the surface downward in the region of their 
greatest activity; as it has been suggested that the limitation of living 
reef-builders to twenty fathoms may be a thermal one. 
Wherever any anomaly of temperature presents itself, the condition 
of such anomaly should, if possible, be ascertained. Thus there is rea- 
son to believe that the cause of the temperature of the surface-water 
being below that of the subsurface stratum, in the neighborhood of 
melting ice, is that the water cooled by the ice, by admixture with the 
water derived from its liquefaction, is also rendered less salt, and there- 
fore floats upon the warmer and salter water beneath. Here the deter- 
mination of specific gravities will afford the clue. In other instances a 
warm current may be found beneath a colder stratum; and the use of 
the “ current-drag”” might show its direction and rate. In other cases, 
again, it may happen that a warm submarine spring is discharging itself, 
as is known to occur near the island of Ascension. In such a ease, it 
would be desirable to trace it as nearly as may be to its source, and to 
ascertain its composition. 
Movements of the Ocean.—The determination of swrface-currents will, 
of course, be a part of the regular routine, but it is particularly desira- 
ble that accurate observations should be made along the line of sound- 
ing in the Southern Ocean, as to the existence of what has been de- 
scribed as a general “southerly set” of oceanic water, the rate of which 
is probably very slow. It is also very important that endeavors should 
