456 



NATURE 



[March 13, 1884 



it. We can only mention here the very interesting sketch 

 given by M. Nathorst of the relations of the Japanese 

 flora to those of different parts of the Pacific basin; the 

 paper ought to be translated in full in some language 

 more familiar to the geologists of Western Europe. The 

 memoir contains the description of seventy species of plants 

 from Mogi, seven species from the coal-measures of Taka- 

 sima, and seven species from the plants in the Berlin 

 Museum. The descriptions are accompanied by si.xteen 

 plates. 



Two other important papers, both in English, are con- 

 tributed to the same volume by M. Otto Petterson. One 

 of them embodies a general discussion, an account of 

 which appeared in N.\TURE, vol. xxviii. p. 417, on the 

 properties of water and ice between - 20° to + 15° Cels., 

 on the ground of the author's own measurements. The 

 second paper, " Contributions to the hydrography of the 

 Siberian Sea," not only contains valuable information 

 gathered from the very numerous measurements of 

 depth, saltness, and temperature of water during Nordens- 

 kjold's expeditions on the Kara Sea and along the 

 Siberian coast, but also gives a most valuable sketch of 

 the hydrography of the Kara Sea. It seemed that 

 nothing new could be written on this northern IVIediter- 

 ranean Sea after the beautiful researches by Dr. Petter- 

 mann based upon the recent researches of the Norwegian 

 seal-hunters. Still Mr. Petterson introduces a new 

 element into the discussion, namely, the influence of 

 the warm water poured into its basin by the Siberian 

 rivers. During the summer the Kara Sea north of the 

 Obi and Yenisei is covered with a layer of almost fesh 

 water which has a depth of neaily twenty metres in 

 the south, and a temperature of 6^ to 9^ Celsius in the 

 summer. This layer thins out and becomes cooler as 

 it advances towards the north, but still it reaches the 

 north-eastern extremity of Novaya Zemlya, where it meets 

 with the salt oceanic current brought along the western 

 coast of the island. On the other hand, the middle parts 

 of the Kara Sea are invaded by the Arctic current bring- 

 ing cold and much Salter water from the north-east. 

 It passes underneath the fresh-water current and reaches 

 the surface about the middle of the Kara Sea, where a 

 saltness of 3 03 has been observed. This cold current, 

 which has in the deepest parts of the Kara Sea (lOO to 

 222 metres) a temperature slightly oscillating between 

 - i"'4 to - 2°o, and a saltness of 3'i9 to 3 '49, is healed 

 more or less on its surface, which reaches in the summer 

 from 2° to 4" above zero in the south-western and north- 

 eastern parts of the Kara Sea : whilst in the middle, even 

 on the surface, the temperature is generally about zero, 

 or even — o^'S. This distribution of currents explains the 

 very slow melting of ice in the middle parts of the Kara 

 Sea, which Dr. Pettermaun compared to an ice-sho.al 

 floating in the middle on the surface of our ponds after a 

 free channel has been opened along its coasts. Two 

 maps on a large scale, sho>ving the distribution of tem- 

 perature and saltness in the Siberian Sea from Novaya 

 Zemlya to Behring Strait, and embodying the results of 

 Nordenskjold's determinations of latitudes and longitudes 

 on the Siberian coast, accompany the papers of M. 

 Petterson. 



We find in the same volume an elaborate paper, by A. 

 Wir^n, on the Cha^topods of the Siberian and Behring 

 Seas. Six tables accompany this paper, which contains 

 the description of seventy-three species of Chaetopods. 

 The chief features of this fauna already being known from 

 Nordenskjold's preliminary report, we only notice that 

 the richest part of the Siberian Sea is the Kara Sea, 

 where the Vc^a Expedition and those of 1875 and 1876 

 discovered no less than sixty-nine species, whilst in the 

 remainder of the Siberian Sea only fifty-three species 

 were found until now. 



Finally, we notice in the same volume M. Aug. 

 Wijkander's paper on the magnetic observations made 



during the expedition (in French), and an appendix to 

 the paper on the geographical determinations, by A. 

 Lindhagen. It appears fro.n the former that the mag- 

 netic declination on the coast of North-Eastern Asia 

 presents several anomalies. The position of the isody- 

 nams is quite different from those given on the map of 

 the German Admiralty (" Isodynamen und Werthe des 

 magnetischen Potentials fur 18S0"). As to the inclina- 

 tion, it is but slightly different from the values 

 which would result from Sabine's work ; but the 

 declination differs notably from the values given on the 

 maps both of the German and English Admiralties. For 

 the Behring Strait region this last, however, is decidedly 

 the best, the average corrections for the English map 

 being -2°'l,and - 3^7 for the (German Admiralty map. 

 The errors result from the secular variation having been 

 only calculated, and not yet measured directly. 



The interest awakened by the expedition of the Vega 

 towards the North Siberian .Sea will be perpetuated by 

 this work. The serious scientific spirit in which the dif- 

 ferent departments of natural history are dealt with in the 

 records of the cruise of the Vega will contribute more 

 towards the increase of our knowledge of the Arctic 

 regions than many costlier expeditions. 



The third volume, just published, is mostly occupied by 

 F. Kjellmann's " Alga: of the Arctic Ocean" (430 pages, 

 with 31 plates). This work — the result of the author's 

 ten years' Arctic experierice — not only contains a complete 

 botanical description of all the AlgEe of the Arctic 

 Ucean which came under notice ; the author gives also 

 a general sketch of the .A.rctic marine flora, with its sub- 

 regions ; he discusses the causes which gave it its present 

 character: structure of the coast-line, tides, characters of 

 the bottom, temperature, and so on ; and he endeavours 

 to draw also the chief lines of its evolution, giving thus 

 rich material for solid generalisations. 



Mr. W. Leche cont ibutes to the same volume a note 

 on the forty-two species of Lamellibranchiata brought in 

 by the Vega; Mr. P. T. Cleve describes (in English) the 

 Diatoms collected in the .Arctic Ocean and on the return 

 journey of the expedition, his paper being illustrated by 

 live plates, which figure eighty-four species, mostly new ; 

 and Prof. P. Kramer and IJr. C. J. Neuman describe (in 

 German) thirteen new species of Acarids. P. K. 



EARTH TREMORS 

 C\^ the various movements to which the crust of the 

 ^^ earth is subjeLt, the minute motions called earth 

 tremors attract our attention by their universality. Be- 

 tween them and the other motions which affect the soil 

 the difterence is chiefly in degree. 



Earthquakes are the sudden and violent movements of 

 the ground. Earth pulsations, which may be observed as 

 terminal phenomena of large earthquakes, are movements 

 of considerable amplitude, but so slow in period that 

 without the aid of instruments they may be passed by 

 unnoticed. Earth Oscillations are the secular movements 

 of upheaval and depression evidenced to us by raised 

 beaches, sunken forests, and other geological phenomena. 

 Lastly, we have eanh tremors, or movements quick in 

 period, but which escape our attention on account of the 

 smallness in their amplitude. As these latter are phe- 

 nomena whicli are probably observable in all portions of 

 the globe, and have as )et attracted but little attention, 

 excepting perhaps where they have proved themselves 

 troublesome intruders affecting astronomical and other 

 observations of a delicate nature, I purpose giving an 

 epitome of the more important results which their obser- 

 vation has yielded. 



Earth tremors produced by artificial disturbances, such 

 as the passing of carriages or trains, the movements of 

 machinery or bodies of people, are at our disposal for 



