170 ~=—SsE.. B. Hunt on the Dynamics of Ocean Currents. 
essential for good observations. The facts to be observed 
also of a character so complex and elusive, are so subject 
fluctuation in a given locality, and are involved in movements 
of air and water of so vast compass, that we cannot hope for 
pce of knowledge by the use of means now in 9 l 
he single fact that most observations are made on the wale 
surface while the ocean depths are of vital efficacy in shapinga 
“marine phenomena, gives a character of signal incompleteness 0 
those observations which have been mainly instrumental in it 
ing the received: notions on the system of oceanic circulation 
gravitation, diurnal rotation, a solid nucleus and a homogeneole 
water envelope unbroken by land. This water stratum would 
shape itself so that its bounding surface would be a strictly 
mathematical level surface. A level surface of this natare 
be defined as one which is at each point perpendicular 10% 
resultant of all the forces acting on the individual mole®™ 
situated in that surface. In this case it would be a continu® 
oblate spheroid to which the resultant of gravity and per ‘aa 
entirely continuous, though no more truly — 
the normal ocean level, and it is a useful sur! 
all vertical ocean movements or perturbations. If we 2° 
the homogeneous earth without continents a 
i . 
tor will become a line of maximum heating, from wht 
-— there will be a progressive diminution of heat ane”r 
: This would cause an expansion of the heated waters W™" 
thus rise above the normal level surface by an amount ed" 
