4 Fishery Board for Scotland. 



referred to the action of winds, or to the effect of rainfall, or to direct 

 barometrical pressure, or to other causes of a like nature. The 

 nature and the causes of the fluctuations which mean sea level is 

 subject to during still longer periods, from oue year to another, are 

 at present still more obscure. 



Thirdly, though the connection of this . fluctuation of sea level 

 with fishery problems may be remote, yet it is at least conceivable. 

 A difference in the level of the North Sea amounting to somewhere 

 about 6 inches on the average between May and December, or a change 

 in the whole annual mean sea level of say 3 or 4 inches from one year 

 to another, must involve the transference of an immense body of 

 water, and must appreciably affect the composition and the salinity 

 of the sea itself. It forms some part, at least, of that complex pheno- 

 menon which we seek to study in our hydrographical investigations, and 

 which we may be able some day to correlate with periodic phenomena 

 in the life history and the fluctuating abundance of our food fishes. 



By the kindness of Mr. E. Gordon Nicol, and of Mr. J. Hannay 

 Thompson, the Harbour Engineers at Aberdeen and Dundee, I have 

 had access to a long series of tide records kept at the dock gates of 

 these two ports. The Dundee observations were taken at the dock 

 gates of King William's Dock, the harbom* datum being from the sill of 

 the lock entrance, which is 9'74 ft. below ordnance datum level. 

 Those at Aberdeen were taken at the Victoria Dock gates, the harbour 

 datum being the sill of the lock entrance, which is 14-62 ft. below 

 ordnance datum level. The mean sea level at Dundee from 1897 to 

 1912 is found to be 10*39 ft. above harbour datum ; i.e. "65 ft. above 

 ordnance datum. Mean sea level at Aberdeen for the same period, 

 and also for the entire period 1862-1913, was found to be in each case 

 15"60 ft. above harbour datum ; i.e. '98 ft. above ordnance datum. 

 This discrepancy, amounting to '33 ft. between the height of mean 

 sea level in relation to ordnance datum at Dundee and Aberdeen, 

 is not explained. It is, however, precisely aldn to similar local differ- 

 ences of level that have been detected on the coast of France, for in- 

 stance, and in many other parts of the world, as described by Kriimmel 

 (op. cit. p. 64) and other writers. It is very noteworthy that the 

 direction of the prevailing current on our East Coast, from North to 

 South, corresponds to this observed fact of the higher mean level of 

 the sea at the northern, as compared with the more southern, station. 



Mr. Gordon Nicol tells us that at Aberdeen he assumes high water 

 of ordinary spring tides as 22 ft. and low water of ordinary spring 

 tides as 9 ft. 3 in. above harbom* datum. The mean of these two, 

 viz. 15-625 ft., agrees as nearly as possible with the mean value that we 

 have found for the tides as a whole. The Aberdeen records run 

 from the beginning of the year 1862 to the end of 1913, with only a 

 single break of three months, from March to June 1875 ; those of 

 Dundee begin with the year 1897, and go on continuously to the 

 present time, but they have only been worked up to the end of 1912. 

 In both cases the observations give the height of the tide at high 

 and low water. They are simply made by eye, to the nearest inch, 

 upon a vertical scale, no recording tide-gauge being in use. Neverthe- 

 less, the observations have been so carefully and so regularly recorded, 

 and the consecutive period over which they extend is so long, that 

 they seem well adapted for throwing light upon our problem. 



