ON TIDES. 299 
Tides.— Report of Committee to assist work on the Tides (Professor 
H. Lamp, Chairman; Dr. A. T. Doopson, Secretary ; Col. Sir C. F. 
Cuiosze, Dr. P. H. Cowetu, Sir H. Darwin, Dr. G. H. Fow.er, 
Admiral F. C. Learmonts, Professor J. Proupman, Major G. I. 
Taytor. Professor D’Arcy W. THompson, Sir J. J. THomson, 
Professor H. H. Turner). (Drawn up by the Secretary.) 
1. The process of reduction of the tide-gauge records at Newlyn has not been 
earried much further than is indicated in the Report for 1921, except that ‘ residues ’ 
from a complete year’s record are now available. Further analyses have been carried 
out in the manner indicated in 1921 and revised harmonic constants for the usual 
Darwinian constituents are given later in §6. The residual semi-diurnal oscillations 
are not yet reduced to law and direct analyses of these have not been attempted, 
_ but two hypotheses concerning them have been considered. Further consideration 
] has been given to the shallow water problem, and some conclusions have been 
formulated in §5. 
Friction. 
. The first hypothesis concerning the residue of unknown origin was suggested 
by “Scat Proudman, and he contributes an appendix dealing with the effects of 
friction on tidal motion. The effect of friction is definitely to introduce harmonic 
constituents which are not in the original tidal motion or among the ordinary ‘ shallow 
water constituents.’ ‘ Application of the law suggested by him has been made to the 
Newlyn tides, but so far without much result, the reason for which is probably the 
difficulty of isolating this frictional effect from other and larger perturbations. 
Powerful support for such a hypothesis, however, has been obtained from a study of 
the tides at St. John, N.B., in the Bay of Fundy. Attention was called to the 
relevant features of these by Dr. Bell Dawson, Superintendent of the Canadian Survey 
of Tides and Currents. 
The M, Constituent at St. John, N.B. 
3. The results of analyses for M, for over nineteen years were available, and these 
showed that the amplitude (R) of the constituent varied in a period of nineteen years 
from 9-45 ft. to 9-99 ft. Darwin’s factor f should give H=R'f as the amplitude of the 
_ principal term of this constituent and H should be constant from year to year. It 
was found, however, that H varied in a period of nineteen years from 9-54 ft. to 
10-07 ft. so that the factor f was futile. Dr. Bell Dawson suggested that the theoretical 
factor should not be used for St. John, but that the variation actually found should 
be used to give a new factor for local use. This, of course, would meet the case in 
practice, but the explanation of the behaviour is very important. Investigations 
showed that this constituent M, is effectively composed of three terms of speeds, 
6,6+N, o—N, where o is the speed of the principal term, and N is the rate of revolution 
of the moon’s nodes. Now the full development of the potential* gives no indication 
ot the term with speed c—N, but an explanation of the occurrence in actual tides is 
immediately furnished by Professor Proudman’s theory. 
Unfortunately, there are no long sequences of analyses for British waters, but the 
evidence tends to show that Liverpool * constants ’ are affected similarly to those of 
St. John, while the ‘ constants ' for Indian Ports show the effect in a smaller degree. 
‘These and other perturbations of harmonic constants due to deficient analyses and to 
secular changes of unknown origin are to be discussed by the Secretary in a separate 
aper. 
**The Harmonic Development of the Tide-generating Potential, by A. T. 
Doodson, D.Sc., Proc. Roy. Soc. (A), vol. 100, 1921. 
