12 



Fishery Board for Scotland. 



obviouf? : the chief difference between the two consisting in a greater 

 amplitude at Dundee, and a retardation of phase, which is about one 

 month later than at Milford (Fig. 5.) 



The phenomenon we are considering was first detected nearly 

 fifty years ago by Lord Kelvin, who, in discussing the records of the 

 Kamsgate Tide-gauge, said, " I also found very decided indications of 

 an annual rise and fall, which seemed to exceed the amount of the 

 solar semi-annual tide, and to make the mean level very sensibly 

 higher in autumn than in spring, an effect probably to be accounted for 

 by an annual period in the amount of water received into the sea by 

 drainage, in the melting of ice, and from the direct fall of rain into 

 it." Mr. Roberts, in an appendix to Lord Kelvin's Report, gives 

 the co-efficients for the two waves as follows (in feet) ; for the annual 

 tide, -127 sin (2t+253°), and for the semi-annual tide, -0748 sin 

 (2t-f-72°). And Mr. Edward Robert's, who, after half a century, still 

 carries on his father's work of tide-prediction, has most kindh^ given 

 me the corresponding formulae for certain other British ports (see p. 14). 



In recent years this annual fluctuation has attracted very con- 

 siderable attention, and accounts of it have been published for various 

 stations, especially in the Baltic and on the German, Dutch, and 

 Norwegian coasts. 



The following figure (Fig. 6), taken from a paper by Professor Otto 

 Pettersson, shows, from month to month, the Mean Sea Level at certain 

 stations on the Dutch and Baltic coasts, while similar results have been 

 arrived at in Norway by Professor Geelmuyden. The general corre- 

 spondence between the curves is very strildng, and with their main 

 features om- curves for Dundee, Aberdeen, and Milford are in general 

 agreement. 



In order to summarise, as briefly as possible, this part of the 

 question, I give the following Table, in which our own results are 

 compared with those given in Professor Kriimmel's Handbuch der 

 Oceanographie, and with certain others given us more recently by 

 Dr. Brehmer and Dr. Rosen. 



Table E. — Monthly Mean Sea Level, in feet, above or below the 

 Mean Annual Value. 



* From Kriimmel, Handb. der Oceanographie, 2nd ed., 1907, vol. i., p. 58. 



t Mean of observations at fourteen German and Danish ports, from Dr. Brehmer, 

 Ann. der Hydrographie, May 1913. 



J Mean of observations at eight Swedish Stations, from Dr. P. C. Rosen, in Svenska 

 Bydrogr. Biol. Ko^mnissionens Skrifter, i., 1902. 



