SPHEROIDS, AND ON THE OCEAN TIDES UPON A YIELDING NUCLEUS. 
35 
we write (as in the report) y, cr for earth’s rotaton and moon’s mean motion, then we 
shall find the following speeds will combine so as to give shallow-water tides indis¬ 
tinguishable from the true fortnightly tide, namely, 2(y—cr) and 2y, also y—2<x and y ; 
and besides there are four combinations of the elliptic tides which give the same 
period of compound tide, if we neglect the motion of the moon’s perigee. It therefore 
seems quite possible that in certain stations the true fortnightly tide may be masked, 
or have its phase largely affected by these compound tides, and this is, perhaps, the 
explanation of the great irregularity in the phases. 
A series of observations in some oceanic island near the Equator, or better still far 
north or south, would be of immense value to decide this point. 
p 
o 
