On the times of high and low tides

The number N of low tides in a given 6‐hour interval of the day varies typically by a factor of order 2. A simple formula is derived relating N max / N min to the ratio R of the solar and lunar semi‐diurnal tidal constituents. This is shown to be quite accurate provided that the diurnal constituents are not large, and that the shallow‐water tides are negligible. Hence R could often be deduced from observations of N max / N min alone, with the aid of only a timepiece.