0)1 Mean Sea Level and its Fluctvations. 



29 



\\\\Q\\ we look at our Aberdeen records for the same years, no such 

 maximum for the year 1899 is at first .siinht apj)arent : but when we 

 observe that the vahies for the wliole period in question are low, and 

 when we reduce them to the mean of the said period (instead of to the 

 mean of the h)n<r period 18()2-19]3) then we find that a maximum i!\ 

 1899 is well marked. And when we smooth all tlie curves, includin.u' 

 that for Aberdeen, then we see without difficulty that their general 

 trend is very similar (Fig. 11). 



From General Madsen's paper, which, as already mentioned, has 

 reached me while this paper of mine is passing through the press, I 

 have compiled the mean annual heights of Mean Sea Level at Copen- 

 hagen, for the years 1890-1911 ; and these are shown in the following 

 Table (Table M.), with and without General Madsen's correction foi' 

 wind. 



Table M. — Mean Sea Level at Copenhagen (in cm.), 1890-1911, com- 

 pared with the mean for the whole period of twenty-two vears : 

 (1) uncorrected, (2) corrected for variations of barometric gradient. 



It will be seen that the high maximum in 1899, already noted from 

 Kiel and the Swedish stations, is here very conspicuous. It is of 

 very considerable interest to see that the correction for wind, or rather 

 for barometric gradient, has but a small effect upon the annual mean 

 values of Mean Sea Level ; this fact is clearly brought out by the 

 annual values (Table M.) which I have deduced from General Madsen's 

 Tables of Monthly Means. On the average, the amplitude of the 

 fluctuation is a little diminished by this correction ; that is to say, 

 the mean departure from zero-level, irrespective of sign, in twenty- 

 two years, is 2'3 cm. in the uncorrected, and 1'9 cm. in the corrected 

 values. But the two series of values run from 1890 to 1911 in very 

 close conformity. Wind, or barometric gradient, is certainly not a 

 direct and potent cause of the variation from year to year of Mean 

 Sea Level. If we compare the Aberdeen values (reduced to the mean 

 of the same period) \vith tliose for Copenhagen, we again see a general 

 trend of similaiity^ in spite of the absence at Aberdeen of the high 

 maximum in 1899, characteristic of Copenhagen and the other Baltic 

 stations. It is a curious fact that from 1890 to 1899 the Copenhagen 

 annual means are almost all above the Aberdeen values, but are 

 almost all below these from 1900 to 1911, 



