June 2, 1910J 



NATURE 



413 



in the waters of Iceland and the Faeroes, the investiga- 

 tions will have a more official character, being carried out 

 at the expense of the Danish Government and as part of 

 the international scheme of w^ork. The second part of 

 the cruise will set out in the beginning of July from some 

 English port. The expenses of this portion of the expedi- 

 tion will be defrayed partly by the Carlsberg Institution 

 of Copenhagen, which does so much for the promotion of 

 science in Denmark, partly from private sources. 



Both in the Atlantic and Mediterranean the expedition 

 will work over waters which have been already, for a 

 great part, investigated by the Thor. It is not proposed 

 to devote much time to the Atlantic region south of 

 Ireland, and there is the less reason for doing so as 

 previous w^orkers, especially the Prince of Monaco, 

 Schmidt, and the Irish investigators, have already done so 

 much there. Nevertheless, a series of deep-sea hydro- 

 graphical observations from the south of Ireland to the 

 coast of Morocco, continuous with similar series from 

 Iceland to Ireland and through the Mediterranean, will be 

 of extreme interest, both in biological matters and as a 

 further contribution towards understanding the circulation 

 of the waters of the Atlantic and the adjacent seas. 



In the Mediterranean, on the other hand, the hydro- 

 graphical and biological conditions are only imperfectly 

 understood. .As is well known, the Mediterranean is an 

 almost completely land-locked and independent ocean, 

 with an average depth of more than looo fathoms, descend- 

 ing at places to 2000 fathoms. This huge basin is con- 

 nected with the Atlantic at the Straits of Gibraltar by a 

 narrow sill or threshold, which is only 200 fathoms deep. 

 Any mixing of the Atlantic water with the Mediterranean 

 wa.t^r can therefore only proceed on the surface, and the 

 renewal of the deeper layers, which is necessary for the 

 development of an abyssal life, and which actually does 

 take place, can only be due to the conditions, evaporation, 

 convection currents, but mostly wind influence, prevailing 

 in the Mediterranean itself. On the other hand, it seems 

 certain from earlier investigations that the deep water 

 of the Mediterranean, which is much more saline than the 

 Atlantic, occasionally or normally wells up over the 

 threshold at the Straits and flows out into the Atlantic as 

 a deep-water current with a northerly direction. A further 

 interesting topographical feature of the Mediterranean is 

 that it is divided into two deep-water basins bv a sub- 

 marine ridge, which stretches across between Sicily and 

 Tunis, and is only about 150 fathoms deep. The circula- 

 tion of the waters within the two deep basins west and 

 east of this ridge must therefore be for the most part 

 independent. The determination of the character of the 

 water in the two basins, in all layers from the surface to 

 the bottom, promises results of more than usual interest. 



The hydrographical observations will be of two kinds, 

 physical and chemical. The temperature and salinity will 

 be determined, as also the direction and strength of the 

 currents, in all depths from surface to bottom, in accord- 

 ance with the most modern methods employed by the 

 international investigations. Entirely new methods have 

 also been recently worked out by Danish men of science i 

 at the Carlsberg Laboratory in Copenhagen for the deter- I 

 mination of the chemical composition of sea water, for 

 example, the dissolved gases (O, N, CO,) and the alkalinitv 

 (concentration of H-ions). It is probable that these new 

 methods will throw fresh light upon the factors determin- 

 ing the differences in the occurrence and appearance of 

 the organic life at different depths and in different waters, 

 differences which the salinity and temperature by them- 

 selves cannot explain. It is obvious that the waters men- 

 tioned in the Atlantic and Mediterranean offer exceptional 

 opportunities for such an investigation. 



On the biological side, the investigations will be on the 

 lines followed by the International Council for the Study 

 of the Sea, and will be directed, in the first place, to the 

 elucidation of the life-histories and biological conditions of 

 the principal fishes. The advantage of making investiga- 

 tions over a wide area, as from Iceland to Morocco and 

 the Mediterranean, is just that the differences in the 

 physical conditions are marked on a large scale, and can 

 be connected directly as cause to effect with the very- 

 distinct differences in the occurrences and biological pheno- I 

 mena of all organisms, from the floating plankton to the 

 NO. 2 II 8, VOL. S;^'] 



fishes. One of the most interesting problems here will 

 thus be to determine the relation between the Atlantic and 

 Mediterranean faunas, how far the latter is dependent, if 

 at all, on the former, and the differences in the abyssal 

 life of the two regions, all in connection with the physical 

 and chemical differences. 



A NEW AMPEREMETER. 



A NEW aperiodic millivolt and amperemeter for con- 

 ■^ tinuous and alternating currents has been brought 

 to our notice by Messrs. Isenthal and Co. The operation 

 of the instrument is based on methods already described 

 by Drude and Klemencic, in which the current to be 

 measured is caused to heat up thermojunctions, thus 

 setting up indirectly a current which actuates the move- 

 ment of the instrument. The novelty in the present instru- 

 ment consists in the arrangement adopted for combining 

 the action of a number of thermojunctions in such a 

 manner that thermocurrents are produced of sufficient 

 magnitude to deflect an ordinary pivoted moving-coil 

 instrument. 



The thermocouples are placed in the four arms of a 

 Wheatstone's bridge, the movement being connected to two 

 opposite corners of the bridge, and the leads carrying the 

 current that is to be measured to the remaining corners. 

 The polarities of the thermocouples are so chosen that when 

 the bridge is warmed up by the passage of a current the 

 electromotive forces set up in the four arms conspire so 

 as to send a current through the movement. The arms 

 of the bridge are adjusted so that the thermoelectric current 

 passes through the movement without entering the external 

 circuit, and the current from the external source passes 

 through the thermocouples without affecting the galvano- 

 meter. 



As the deflections of the instrument depend on the heat- 

 ing effect of the current to be measured, it should give 

 correct readings for direct current or alternating current 

 of any wave-shape or frequency. It seems that sources of 

 error might be introduced by Peltier effects and changes 

 of temperature of the surroundings, and it would be 

 interesting to learn to what extent such errors are appreci- 

 able, and in what manner thev have been compensated 

 for. 



The sensitiveness of the meter is 225 millivolts with a 

 current of i ampere, and its range as an amperemeter can 

 be increased to anv extent bv the use of shunts. 



GEOLOGY OF THE LONDON DISTRICT. 



T^HE Geological Survey cannot well be charged with 

 neglect of London, except in the matter of six-inch 

 maps, a want that will probably be soon seen to. From 

 1864 to 1906 various memoirs were issued which deal, 

 though sometimes only partially, with the geology of 

 London and the neighbourhood. Two of these, however, 

 treat of the whole district and the whole of its geology, 

 and now we have a third, in which the results reached 

 by many workers are given up to date. 



This memoir may be said to have been done by Mr. 

 Woodward to celebrate his retirement from office, more 

 than a year ago, and a remarkably good celebration it is. 

 From its very low price it is within the reach of all 

 students, and we may hope that its author may live to 

 edit many editions. 



The area described is that covered by the lately published 

 four sheets of the new geological map of London, some 

 errors in which are duly noted on pi v. After a general 

 account of the area, five pages are given to an account 

 of the various beds beneath the Chalk, which do not 

 come to the surface here, their presence underground 

 having been proved only by borings. These consist of 

 Devonian rocks, at the base. Red Rocks of doubtful age, 



^ Memoirs of the Geological Sun-ey. The Geology of the London 

 District. By H. B. Woodward, F.R.S. Pp. vili + 142 + plate. (London : 

 Hi< Majesty's S'ationery Office : E. Stanford : Edinburgh : \V. and A. K. 

 Johnston, Ltd. Dublin : Hodges, Figgis and Co., rqcg. Price it. 



