42 U. S. COAST AND GEODETIC SURVEY 
0 si Ont ben Cen males | 6 8 10 12 
Fic. 21.—Tide curve, Los Angeles Harbor, illustrating seiches. 
tabulated from the smooth curve, but note should be made in the column of remarks 
of the time and height of the highest (or lowest) point of the short-period oscillations. 
Smoothing the tide curve must not be carried beyond the legitimate purpose of 
eliminating short-period oscillations. When the tide curve is disturbed in time and 
height by unusual weather conditions, the tabulator may be tempted to substitute for 
the actual tide curve a hypothetical tide curve which disregards the disturbances in 
time and height, on the mistaken notion that better mean values are derived through 
this substitution. A moment’s reflection will make it evident that in such cases it is 
much better to tabulate the data directly from the actual tide curve and reject, if neces- 
sary, the disturbed values from the computation for mean values. 
Tides of Small Range 
For tides of small range—less than half a foot—the tabulation of the hourly 
heights presents no special problems, except that it may be desirable to tabulate these 
heights to the nearest half tenth or even to the nearest hundredth of a foot. But m the 
tabulation of the high and low waters of tides of small range, difficulties are encountered. 
The tide curve is rarely free from the effects of wind and weather. With large 
ranges of tide these effects are generally only a fraction of the range and hence it is 
not difficult to pick out on the curve the high and low waters. But with tides of small 
range the weather effects are frequently of the same or even of greater magnitude than 
the purely tidal range, so that the highest and lowest points of the curve may depart 
widely from the times and heights of the undisturbed tide. 
An even more troublesome feature is that the weather effects may produce more 
than the regular number of high and low waters in a day. It becomes difficult then 
to determine which of these to tabulate as the high and low waters of the day. 
A similar difficulty is presented in tabulating tides of the mixed and daily types 
at times when the higher lows and lower highs tend to merge. At such times the range 
