of the Fishery Board for Scotland. 



335 



the organisms which are suspended in it, and carried by it, especially the 

 diatoms and minute plant life. If, for instance, a series of floating forms 

 which are usually absent from one region and normally abundant in an- 

 other region, suddenly make their appearance in numbers in the former, it 

 offers very strong evidence that there has been a movement of the water 

 from one to the other. This branch of inquiry is being pursued by Pro- 

 fessor Cleve of Upsala, in connection with the investigation of the 

 currents in the North Sea. 



A third method, somewhat akin to the last mentioned, consists in the 

 employment of floating bodies, usually bottles, whose place and time of 

 immersion are known, and which can be subsequently identified when 

 they are recovered. It is a method regularly used in the Atlantic by 

 the United States Hydrographic Office, and by the Deutsche Seewarte 

 of Hamburg. It was also employed by the Prince of Monaco in connec- 

 tion with the' movement of the Gulf Stream* and by various others. f 

 It is the system which has been adopted in the experiments made by 

 the Fishery Board, the results of which are given in the present paper. 

 This mode of ascertaining the direction and rate of surface currents 

 appears at first sight to be simple, and it is comparatively inexpensive, 

 but it may be open to objection on several grounds. In the first place, 

 if the floating body is not completely submerged it will be directly acted 

 on by the wind, which may drive it in a direction different from that of 

 the moving water ; and the extent of the wind-action will largely depend 

 upon the proportion of the surfaces exposed and submerged. In the 

 second place, even although completely submerged, one cannot always be 

 certain of the exact route taken by an individual float between the point 

 where it was put into the water and the point where it was picked 

 up, or as to the time it may have lain upon the beach before being 

 observed, The course may have been irregular or zig-zag, and the 

 lapse of time between the stranding and recovery of the float may 

 be considerable. But the force of these objections may be greatly 

 diminished by due care and by a study of the winds during the period 

 of flotation, and by a multiplication and comparison of the observations. 

 Conclusions based upon isolated experiments may be erroneous, but when 

 the same results are obtained in dozens or hundreds of experiments, ex- 

 tending over a long time, the conclusions to be drawn from them become 

 much more certain. 



Two kinds of floats were employed in the experiments, namely, bottles 

 and slips of wood ; the former gave by far the best results, judged by 

 the percentage of those recovered. The bottles (fig. 1) were made of 

 coarse glass, they were wide-mouthed, and of ounce size, and in each 

 was placed a card bearing a number, and printed directions in three 

 languages — English, Danish, and German — requesting that it should 

 be returned to the writer, with a statement of the place and date of 

 recovery. The card and the cork were clipped in melted paraffin-wax, and 

 the buoyancy of each bottle was tested in a pail of sea water. Soft lead 

 wire was then wound round the neck, sufficient to submerge the bottle 

 flush with the surface ; in a few cases where it was exceptionally heavy, 

 cork was tightly tied to it by silk cord (which has been proved to resist the 

 action of sea water for years) until the same degree of buoyancy was 

 obtained. The slips of w r ood (fig. 2) were six inches long, one inch broad, 

 and | of an inch thick. They were immersed in melted paraffin, the 

 printed card, also coated with paraffin, and a small square piece of 



* Sur le Gulf Stream, Recherches pour etablir ses rapports avec la cote de France, 

 1885 ; and various subsequent papers in the Comptes rendusde V Acaddmic dcs Science. 

 t M. J. Thoulet, Oceanographic, premiere partie, 1896. 



