D4) U. S. COAST AND GEODETIC SURVEY 
inequality. But for technical purposes it is of obvious advantage that some definite 
criterion be available to separate the two types of tide. 
Since diurnal inequality in the tide arises from the interaction of daily and semi- 
daily constituents, the criterion employed for defining type of tide makes use of the 
magnitudes of these constituents. A formula frequently used, which is based on the 
harmonic constants of the tide, is the ratio of K,+O, to M,+8,. In this formula, 
K, and O, represent the amplitudes of the principal daily constituents of the tide, and 
M, and 8, represent the principal semidaily constituents. Where this ratio is less than 
0.25, the tide is classed as semidaily; where it is between 0.25 and 1.50 the tide is classed 
with the mixed type; and where it is greater than 1.50 it is classed with the daily type. 
To exemplify the use of this formula, we may employ it to determine the ratio 
of K,+0, to M;-+S, for the tides used in the preceding pages to illustrate the different 
types. For New York this ratio is 0.18, for Pensacola 10.5, for Honolulu 1.04, for 
Seattle 0.97 and for San Pedro 0.77. Since the ratio for New York is less than 0.25 
the tide there is classed as belonging to the semidaily type. The ratio for Pensacola 
is more than 1.50 and the tide there is therefore of the daily type. For Honolulu, 
Seattle and San Pedro the ratio is between 0.25 and 1.50 and the tide at those places is 
therefore of the mixed type. 
When harmonic constants of the tide are not available, a rough approximation ~ 
to the ratio of K,+0O, to M,-++S, can be derived from the mean values of the inequalities 
and range of tide. Approximately (K,+0O,)+(M,+S,) can be taken as equal to 1. 4 
(DHQ+DLQ)=Mn, where DHQ. and DLQ are the mean values of the high water 
and low water inequalities and Mn is the mean range of the tide. The derivation of 
the mean values of these quantities will be considered later. 
