210
X
OCEANIC CURRENTS
action of the heavenly bodies we get deviations of the mean
sea-level from the mean level surface amounting to to
metre, and currents of such magnitude as can be produced by
these differences of level. Though we are unable to state the
magnitude of these currents, yet we can conclude that they
are about equal in magnitude to those which are due to differ-
ences of temperature. For the differences of temperature may
indeed cause variations of the sea-level from the mean level
surface up to several metres; but only a small fraction of
this height will give rise to currents at all, and only a small
part of this fraction will cause currents flowing from east to
west.