December 24, 1908J 



NA TURE 



225 



circuits to be tuned accurately in order to obtain the 

 clearest signalling^. 



Whilst this is "the first State-owned station to be 

 used for public purposes, it may be mentioned that 

 the Marconi Company owns eight such stations which 

 have been open for public communication since the 

 Radio-telegraphic Convention came into force. It will 

 be recollected that the Marconi Company somewhat 

 strongly opposed this convention before ratification 

 on the ground that it would destroy the business which 

 they had built up, an opposition which, as we pointed 

 out in Nature at the time, appeared to be short- 

 sighted and against the public interest. It is gratify- 

 ing to learn that the company has loyally accepted the 

 convention, and has steadily cooperated with the Post 

 Office in carrying out its provisions, with what are 

 stated to be beneficial results both for the company 

 and the public, the traffic dealt with having increased 

 in volume and the ships carrying Marconi apparatus 

 having increased in number. Everyone will welcome 

 this further evidence of the development of the utility 

 of wireless telegraphy. M. S. 



SWEDISH HYDKOGRAPHICAL AND FISHERY 

 IN VESTIGATIONS.' 



ALTHOUGH it did not need the existence of an 

 International Council to point out the field for 

 ph)'sical and biological research offered by the waters 

 of the Baltic, there is no doubt that during the last 

 few years of cooperative investigation great strides 

 have been made in our knowledge of the hydro- 

 graphical and correlated biological conditions of this 

 sea, which presents phenomena of peculiar interest 

 which do not exist in the case of the more economic- 

 ally important North Sea. 



The third volume of the " Svenska Hydrografisk 

 Biologiska Kommissionens Skrifter " contains the re- 

 sults of the investigations made by the Swedish men 

 of science Pettersson, Trybom, Schneider, and 

 Broch, up to the end of igoy. 



The first-named describes and discusses at some 

 length the results of his observations upon the water- 

 circulation between the ocean and the Baltic, for the 

 proper understanding of which it is necessary to 

 measure the force of the in- and outgoing currents 

 at the entrances to this sea. This the author has 

 carried out by the use of his " Universalsinstrument," 

 an apparatus designed to indicate the direction and 

 velocity of the current, and, at the same time, to take 

 plankton and water samples at a particular depth. 

 The chief determinations were made at stations in the 

 Great Belt at depths of 5, 10, 20, and 30 metres. In 

 general, the water circulation in this channel consists 

 of an outflowing surface current of low salinity and 

 an undercurrent of high salinity entering from the 

 Kattegat, with an intermediate layer of " mixed " 

 water. Pettersson's work has shown in definite 

 terms the various degrees to which these different 

 layers are affected by the influence of daily tidal 

 movements and also by the annual oscillation of 

 Atlantic water — the Gulf Stream flood — and his chief 

 result is to demonstrate that these oceanic factors are 

 of far greater importance in their effect upon the 

 water circulation of the Baltic than had hitherto been 

 suspected from surface observations. In general, the 

 water-layers at 10 m. and 20 m. depth move in oppo- 

 site directions, except at the time of strongest ebb- 

 tide, when the whole of the water moves seaward. 

 For example, a series of observations at a station in 

 the Great Belt give during flood-tide at 10 m. depth 



1 " Svenslta Hydrografisk Biologiska Kommissionens Skrifter III." 

 (G.-,teborg : Wald. Zachrissons Boktryckeri A.-B.,i9o8 ) 



an average velocity of 80 cm. per second from south 

 to north, and at 20 m. depth an average velocity of 

 27.6 cm. per second from north to south ; during the 

 ebb-tide an average velocity of 69-2 cm. per second, 

 and at 20 m. of 9-7 cm. per second, both the latter being 

 from south to north. The boundaries between water- 

 layers of certain salinity are not horizontal, but the 

 masses are wedge-shaped and are much closer to- 

 gether in the Kattegat than in the inner sea. The 

 surface movements of the Baltic do not depend so 

 much upon the influence of fresh-water supplies from 

 the rivers, but are the results of forces set up by the 

 intrusion below of ocean water of greater density, the 

 effect of which is to cause a circulation of water from 

 the lower layers to the surface. The interesting cir- 

 cumstance that the dissolved oxygen in the surface 

 water is of distinctly greater amount in the inner 

 (northern) Baltic than nearer the southern entrances 

 is explained by reference to the fact that the southern 

 water has a longer course as an undercurrent than is 

 the case in the northern Baltic. The Little Belt was 

 found to consist of " mixed " water practically 

 homogeneous in temperature and salinity, the flood-tide 

 passing the channel with almost equal velocity at all 

 depths, while the ebb is swiftest at the surface. The 

 Sound showed only one outflowing current of 

 homogeneous Baltic water. 



It is in their relation to hydrographical conditions 

 that Dr. Schneider's observations on the distribution 

 of pelagic eggs and larvas of the food-fishes are of 

 special interest. Under the particular physical con- 

 ditions which prevail in the Baltic, the vertical dis- 

 tribution of these forms is characteristic. Pelagic 

 teleostean ova were taken at considerable depths and 

 were practically absent at the surface. Variation in 

 depth distribution was shown for different species, and 

 the same species was found at different depths in dif- 

 ferent months, while larvae occurred, on the whole, 

 nearer to the surface than the ova. The possibility 

 of the existence of cod-larvas in the northern waters of 

 the Baltic is proved by new positive evidence of their 

 occurrence, though in no great numbers, and a pre- 

 viously accepted theory that they only immigrate at 

 a later stage is corrected. On the other hand, while 

 it has been stated that the plaice stock of the Baltic is 

 self-contained and needs no replenishing from other 

 seas, the writer especially notes the absence of plaice 

 larvae from the catches of the Swedish expeditions, but 

 draws no conclusion from this negative evidence, and 

 leaves open the question as to whether, and at what 

 stage, there is an immigration of plaice fry from the 

 west. 



Trybom contributes additions to the record of ex- 

 periments with marked flat-fish and lobsters, and in 

 collaboration with Schneider describes experiments 

 with marked eels which have given interesting 

 results. The eels showed practically without excep- 

 tion an oceanward tendency in their migration, mov- 

 ing in a southerly and westerly direction along the 

 Swedish coast and through the Sound. The high 

 rate of 104 km. travelled in two days was shown by 

 one fish, and ten out of the 63 re-captured, from a 

 total of 300 liberated, travelled at an average rate of 

 more than 20 km. per day. Incidentally, these experi- 

 ments tend to prove the assertion of fishermen that 

 bright moonlight is unfavourable to the capture of eels. 



The result of a long series of observations made by 

 Trybom in the river Dalelf upon the piscine enemies 

 of salmon and trout ova is to brand the grayling as 

 by far the most guilty of spawn-devourers. Small 

 trout prev upon the ova of their own and other 

 species of Salmonida?, and Coregonus, particularly 

 when " spent," is destructive to its own spawn, 

 though seldom found with salmon or trout eggs in its 



NO. 2043, VOL. 79] 



