434 



NA TURE 



[March 8, 1906 



is CoCI^NH,, but only two-thirds of its chlorine 

 can be precipitated. In praseo-cobalt chloride, 

 CoCl 3 .4NH 3 , only one-third of the chlorine reacts as 

 an ion, whilst the compound CoCl 3 .3NH 3 is not 

 ionised at all. 



Now, according to Prof. Werner, the coordination 

 number of cobalt in all these compounds is six, that 

 is to say, the cobalt atom is in all cases associated 

 with six groups or atoms. Outside this are the 

 negative ions. The valency of the positive ion 

 diminishes as the electronegative element in it is 

 increased. Thus we have the following series of 

 compounds : — 



[Co(NH 3 ) 6 ]"'CI 3 ; [Co(NH 3 ) 5 Cl]"Cl,; [Co(NH. ) ) 1 CI.,]'Cl ; 

 and [Co(NH 3 ) 3 Cl 3 ]°. 



It will be seen that here again the essence of the 

 theory lies in the idea of coordination or association 

 as distinct from ordinary valency with its separate 

 linkages. The same ideas may be extended to water 

 of crystallisation in hvdrated salts. 



This slight sketch will, it is feared, give but a poor 

 idea of the ingenuity and comprehensiveness of Prof. 

 Werner's theory, but it is all that the limits of space 

 allow. The book before us may be strongly com- 

 mended to all who are interested in the development 

 of chemical theory, and though, no doubt, the new 

 doctrine cannot by any means be called unexception- 

 able, there is much in Prof. Werner's book that is 

 interesting and stimulating quite apart from the 

 clear exposition of the particular views it is in I ended 

 to disseminate. A. Smithells. 



THE DANISH FISHERY INVESTIGATIONS. 

 Meddelelser fra Kommissionen fra Havatulersogelsen. 



Serie Hydrografi, Bd. i., Nos. 7-S ; Seric Fiskeri, 



Bd. i., Nos. 4-8; Serie Plankton, Bd. i., No. 3. 



(Kcibenhavn, 1 Kommission Hos C. A. Reitzel, 



1905O 

 T^HE reports issued by the Danish section of the 

 J- International Fisheries Investigation Organis- 

 ation deal to a greater extent with purely biological 

 matters than do the publications of the corresponding 

 British committee. Thus of the present instalment of 

 reports two relate to hydrographical researches, one 

 to plankton studies, while five deal with the life- 

 histories of species of fishes of economic importance. 



The hydrographic reports consist of an investigation 

 by Mr. J. P. Jacobsen on the solubility of oxygen in 

 sea-water, with a description of the methods and 

 apparatus employed. Mr. J. N. Nielsen also con- 

 tributes an account of several hydrographic cruises 

 made by the Thor in the summer of 1904 on the 

 north coast of Iceland, and a discussion of the results 

 obtained. The sea-water on the north coast of Ice- 

 land is derived from warm Atlantic water in the 

 Denmark Strait— the Irminger current— and from 

 much colder, but lighter, water of Arctic origin, which 

 comes from the East Greenlandic polar current. The 

 climate of the North Icelandic coast is dependent to 

 some extent on the relative distribution of these two 

 contributing currents. The Irminger current flows 

 NO. 1897, VOL. 73] 



north along the west coast of Iceland, and then, as a 

 result of the earth's rotation, along the north coast. 

 This latter cause, and also the interference of the 

 East Greenlandic polar stream, produce a further 

 rotation of the current, so that it may even round 

 the north-east coast of Iceland and flow south. Along 

 its whole course the Irminger current yields up heat 

 to the atmosphere, cooling by convection as it does 

 so, so that even the lower layers give up their heat. 

 Land-water, produced by the melting of ice and snow 

 masses, cools down the coastal waters, and, being of 

 lower salinity, causes a surface current seawards 

 during the summer and an undercurrent landwards. 

 In winter the lower temperature of the land cools the 

 sea-water, which then sinking in consequence of its 

 greater density, flows seawards as an undercurrent, 

 while it is replaced bv a surface current moving 

 towards the land. 



The distribution of the comparatively warm Ir- 

 minger current is affected by the presence of drift 

 ice; in those years when drift ice is abundant on the 

 Icelandic coasts, the cold (though less dense) Arctic 

 water spreads over the surface, and blocks to a vari- 

 able extent the eastward passage of the Atlantic water. 

 But it also prevents the conduction of heat from the 

 latter to the atmosphere, and as a result, during these 

 hard ice years, the mean temperature of the air of 

 the first six months of the year is much lower than 

 in those years when drift ice is absent or less abundant 

 during the months in question. In this connection 

 the suggestion that telegraphic cable communication 

 with Iceland, and a coast telegraph line, should be 

 established is of considerable interest, for the advent 

 of the ice can usually be foretold by observations of 

 the temperature of the sea. 



Not only does the temperature of North Iceland 

 during the winter depend on the distribution of the 

 eastern branch of the Irminger current, but the 

 fisheries vary in an analogous manner. This appears 

 to be the case with the great herring fishery, and cod 

 appear also to travel to the west, north, and east of 

 Iceland with the current, not appearing in abundance 

 until the temperature of the water reaches a certain 

 value. The pelagic larvae of the latter fish are also 

 distributed by the current, as well as by the offshore 

 and inshore movements of the water due to the cause 

 mentioned. 



A short note by Mr. C. G. J. Petersen on the 

 occurrence of Leptocephali is of exceptional interest. 

 It is well known that finds of this stage of the 

 common eel have been very rare in northern waters. 

 Dr. Petersen tells us that it occurred to him to look 

 for these larvae in warm and deep Atlantic water, 

 using special fishing apparatus. Accordingly in May, 

 1904, Dr. J. Schmidt found a typical Leptocephalus at 

 a station south-west of the Faeroe Isles, in water more 

 than 1000 metres in depth, and in a postscript it is also 

 added that great quantities of Leptocephalus brcvi- 

 rostris have been found by Schmidt " in the depths of 

 the Atlantic," presumably near the same place. Dr. 

 Petersen concludes that it is here, not in the Baltic 

 or North Seas, that the eels of Northern Europe breed, 

 passing in their migrations either the North Sea or 



