8 THE ANTARCTIC MANUAL. 
II. 
TIDAL OBSERVATIONS. 
By G. H. Darwiy, F.R.S. 
Tur dynamical theory of the tides on an ocean lying on a rotating 
planet presents a problem of such difficulty that mathematicians 
have hitherto only succeeded in obtaining a solution where the ocean 
covers the whole planet, or where it is bounded by coasts which 
follow parallels of latitude round the whole circumference of the 
planet. Moreover, success has only been attained where the depth of 
the ocean is constant as we travel along a given parallel, although it 
has been found possible to conceive the depth as varying with the 
latitude according to some simple law. The conditions thus postu- 
lated by the mathematicians are clearly very different from those 
which obtain on the earth, and it might seem at first sight as if 
science could merely record a failure in the presence of the tidal 
problem. This is, however, very far from being the case, for by 
methods depending in part on theory and in part on observation, it has 
been found possible to make accurate tidal predictions and to learn 
much about the tidal oscillations of our complex system of oceans. 
But this is not the place in which to pursue further this branch of 
our subject, and we have only drawn attention to these considerations 
because they indicate the peculiar importance of tidal observation in 
the Antarctic Ocean from a scientific point of view. This region is 
the only one on the earth in which those conditions are even approxi- 
mately fulfilled in which a complete dynamical solution has been 
attained, because here only do we find an ocean uninterrupted 
throughout the whole circumference of the planet. It is true that the 
existence of the Pacific and Atlantic Oceans must introduce con- 
ditions which differ widely from those postulated by the theory, but it 
must clearly be important to obtain observations in an ocean which 
conforms, although roughly, to the theoretical standard, especially 
when we know that observations in this region are almost entirely 
wanting. 
