16 REPORTS ON THE STATE OF SCIENCE.—1918. 
of sight. There are many cases where the harmonic constants have 
not been determined with all the accuracy obtainable. 
2. Harmonic analyses, and possibly more extended observations, 
relating to oceanic island stations appear to be wanting. These would 
probably give results of great theoretical value. 
3. Continuous observations of tidal heights at off-shore stations are 
especially desirable, both as a test of hypotheses relating to the main 
tidal movements and as a foundation for more complete syntheses of 
tidal facts. 
4. Further continuous observations of currents are also desirable. 
The only British observations of this kind which have been analysed 
appear to be those taken in and near the North Sea in connection with 
the ‘‘ Conseil permanent international pour ]’exploration de la mer.’’ 
5. Greater accuracy seems attainable in the harmonic analysis, 
more particularly, of the smaller semidiurnal and diurnal tides. When 
a year’s record is treated by the methods in common use, only the 
numbers obtained for the larger tides can be assumed to be reasonably 
correct. Improvement may be sought by allowing for imperfect isola- 
tion of the different series. This is done by the U.S. Survey, but 
revised methods appear necessary except for the principal solar series. 
6. Accurate determinations of the constants for the long-period tides 
of astronomical origin are much wanted, on account of the part which 
these tides play in various speculations. The numbers obtained by 
analysis of a single year’s record are very uncertain, not through 
defect in the method of reduction, but in consequence of meteorological 
disturbances in the record itself. The analysis of observations extend- 
ing over a long series of years might be expected to give more trust- 
worthy results. 
7. A comparative study should be instituted of the geographical 
distribution of well-attested harmonic constants for tides of different 
periods. This might lead to an improved dynamical conception of 
the great tidal movements. 
8. A knowledge of the free periods of oscillation of the ocean, 
or of special regions of it, would be of the greatest interest, not 
only for its own sake, but as a basis for dynamical reasoning on 
the actual forced tides. It is not known whether any attempt has 
been made in this direction by an examination of the results obtained 
for different ports whose harmonic constants have been accurately 
determined when the predicted tide is subtracted from the observed. 
The residue might conceivably yield some indications as to the longer 
free periods. A further examination of the records attending such a 
disturbance as that of the Krakatoa explosion might also be fruitful. 
