On Mean Sea Level and its Fhtet nations. 



23 



determined it after applyiiiii to their data the correction for wind, 

 and this I am at present nnahle to do ; but there seems no reason 

 why, over a consideiablc period, the 14-months' oscillation should 

 not be demonstrable without this cori'ection. 



Between the dates 1897-1913, 1 have set down, both for Aberdeen 

 and Dundee, the monthly values of Mean Sea Level in successive 

 series of 14 consecutive months : giving not the actual height according 

 to observation, but the difference between that value and the long 

 period mean for the month in question. Taking 14 such periods 

 in the case of Aberdeen (1897-1913) and 13 in the case of Dundee 

 (1897-1912), I obtain the following mean values, in which a somewhat 

 regular fluctuation is at once obvious. 



Table J. — Mean Heights of Mean Sea Level, in fourteen consecutive 

 months from January 1897, in feet (differences between observed 

 heights and long-period mean values). 



The harmonic formulae corresponding to these 14 equidistant values 

 are as follows, in feet (epoch January 15) : 



Aberdeen . . -036 + -046 sin (t+ 40°). 



Dundee . . -033 + "034 sin (t + 18°). 



or in centimetres : 



Aberdeen . . 1-10 + 1-40 sin (t+4U°). 



Dundee . . l-OO-f-1-04 sin (t + 18°). 



It will be seen that the amplitudes, though still very small, are 

 somewhat greater, in fact, about twice as great, as those which the 

 Danish writers have discovered. 



In the following diagram (Fig. 7a), I show, for Aberdeen, the 

 smoothed values of Mean Sea Level dming the 14-monthly period, 

 together with the sine curve calculated therefrom. It will be seen 

 that the agreement is fairly good ; but it must at the same time be 

 remembered that the observed values have been subjected (as also 

 in General Madsen's work) to a considerable process of " smoothing." 

 It seems to me certain that General Madsen has succeeded in demon- 

 strating, and even in measuring, this 14-monthly oscillation as regards 

 Mean Sea Level from his Danish Observations, and I think it probable 

 that, in a preliminary way, I have demonstrated it also for Aberdeen ; 

 but if my preliminary work has shown the existence of such a wave, 

 I do not for a moment suppose that it is exact enough to determine 

 its magnitude. We must always remember, as will be pointed out 

 again in a later part of this paper, that the variations of Mean Sea 

 Level are the resultant of a very large number of causes, which um'te 

 in producing a fluctuation of very great complexity. The small 

 harmonics, of one period or another, which we can extract from the 



