22 Fishery Board for Scotland. 



waves are slightly less than those which I have worked out from the 

 figures given by Dr. Brehmer, and this may be due, in part at least, 

 to the preliminary process of smoothing which their figures appear 

 to have undergone. 



Thus the mean of their determinations of the half-amplitude of 

 the annual wave at nine stations (excluding Giedser) is 7"37 cm., 

 while the mean at the same stations, according to my rough calculation, 

 is 7'84 cm. ; and in like manner the mean of their values for the 

 semi-annual wave is 2 "97 cm., mine being 3 '42 cm. The differences 

 are not very large, and the results for the individual stations are 

 entirely consonant. {See Table N, p. 30, and Table F, p. 14.) 



In the next place, following the lines set forth by Mr. la Cour, 

 they give for the various stations similar formulae, corrected for the 

 influence of wind : that is to say, reduced to the hypothetical con- 

 dition of no barometric gradient, or of absolute calm. As will be 

 seen from Table N, while in all cases the amplitude of the wave, both 

 annual and semi-annual, is diminished by this correction, the diminution 

 is not relatively very great, or, in other words, the annual and semi- 

 annual tides remain with their main featm'es unimpaired. While 

 the mean amplitude, uncorrected, of the annual wa.ve at nine stations 

 is 7'37 cm., the corrected value is 6"60 cm., and again the mean value 

 of the semi-annual amplitude is found to be 2"97, which, when corrected, 

 falls to riO cm. It will be noted that the correction produces a much 

 larger effect upon the semi-annual than upon the annual wave. 



In Table N, the value A^ is referred to the zero-level of the Danish 

 Geodetic Sm-vey. It will be seen that this value is greatly altered 

 by the correction for wind, the latter factor being found to raise the 

 Mean Sea Level of the Danish Cbast in a marked degree. The Mean 

 Sea Level of the nine stations is found to be 0"032 cm. above the Survey 

 base ; but when corrected for wind, it is no less than 7*84 cm. below it. 



Lastly, and again following out a suggestion of Mr. la Com-'s, the 

 wi'iters have found it possible to correlate a portion of the fluctuation 

 in Mean Sea Level with the actual variation in latitude caused by the 

 changing position of the earth's axis. There is a small periodic move- 

 ment of the earth's pole, whose period is about 14 months or more, 

 nearly 431 days ; and taking the Mean Sea Level at nine Danish stations 

 for the years 1891-1911, the writers have discovered a small fluctuation 

 of identical period with the polar oscillation. 



The harmonic formula? which they find for these fluctuations are 

 as follows : — 



(1) For the 431-day period of Mean Sea Level (1) (in cm.) — 



m 



= - 0-009 -I-0-643 sin (m z-55°-03). 



(2) For the 431-day period of variation of latitude (p) (in seconds 

 of arc) — 



a^"^)= -0-009 +0-159 sill (mz-18"-29). 



It will be seen that, while this fluctuation is of very great theoretical 

 interest, the amplitude of the wave is so small (1-29 cm. or '042 ft. 

 for the total amplitude) that it still leaves unaccounted for the greater 

 part of the total fluctuation in sea-level. 



Small as the amplitude of this fluctuation is, I think that it can 

 also be discovered on our own coasts. The Danish authors have 



