Jan. II, 1877J 



NATURE 



237 



those who lake an interest in the pi ogress of geography 

 will doubtless think with us that such an exhibition adds 

 one more to the many attractions of Paris ; now that the 

 Loan Collection is closed, nothing at all approaching it 

 exists in London. 



TEMPERATURES AND OCEAN CURRENTS IN 



THE S O UTH PA CIFIC 

 T N the Annalen der Hydrographie und jnarttwteti Me- 

 ■*■ ieorologie (Jahrg. iv., 1876, Heft 6, p. 219), Herr von 

 Schleinitz, a member of the recent expedition in the 

 German corvette Gazelle, states his views on ocean tem- 

 peratures and currents ; these are somewhat different from 

 those expressed by Sir C. Wyville Thomson (Proc. Roy. 

 Soc, vol. xxiv.), which are based on the data obtained 

 during the Challeui^er expedition. The Gazelle, after 

 leaving Auckland (New Zealand), pursued a course 

 almost due north as far as the Fiji Islands ; thence 

 she proceeded to the Samoan Islands, situated at a 

 short distance north-east of Fiji. After a brief excursion 

 to the Tonga group and back, the Gazelle (from long. 

 172° i8'-5 W., and lat. 14° 28'-! S.) sailed some 2,500 

 nautical miles in a south- south-east direction (to long. 

 141° ii'-4 W., and lat. 45° 33'-6 S.), after which she took a 

 due easterly, and later on, a south-easterly course, to 

 Magellan's Straits (long. 80° 3o'-3 W., lat. 51° 4i'-6 S.). 

 The observations of temperature on the long cruise be- 

 tween the Samoan Islands and the Magellan's Straits 

 are of special interest, as the course taken by the Gazelle 

 hes to the south of that pursued by the Challens^er. 



On the first part of the course described, which has a 

 direction nearly coinciding with the meridian, eight series 

 of observations of temperature were made. The bottom 

 profile of this part shows a peculiar absence of elevations, 

 which is all the more remarkable when compared with any 

 similar profile of the same length in the Atlantic. 



The conclusion arrived at by Herr von Schleinitz, and 

 based on the results of his observations is, that in the 

 Pacific the arctic deep-sea current crosses the equator in 

 a southerly direction and meets the antarctic current 

 only between lat. 30° and 36° S. This is just the reverse 

 of what takes place in the Atlantic, as it seems highly pro- 

 bable from the observations of both the Challenger and 

 the Gazelle expeditions, that in the Atlantic the antarctic 

 deep-sea current passes the equator, running northward of 

 the same to a considerable distance. 



Herr von Schleinitz concludes from these latter ob- 

 servations, that if the antarctic deep current enters the 

 North Atlantic, even as a current of limited breadth, it 

 must nevertheless carry enormous quantities of water from 

 the South Atlantic to the North Atlantic, as it is certain 

 that the current has a depth of more than 1,000 fathoms on 

 the average. He then asks the question. What becomes 

 of this mass of water ? There is no strong surface current 

 in existence which carries it back to the South Atlantic ; 

 even the current caused by the south-east trade winds 

 runs more towards the Gulf Stream than towards the Bra- 

 zilian coast current. There seems only one hypothesis 

 possible, viz., that a great part of the water flows through 

 the Arctic Sea and Behring's Strait into the North Pacific, 

 and that may be the cause of the preponderance of the 

 arctic current of this ocean over its antarctic one. 



The natural conclusion drawn from this is that the 

 South Pacific, in order to complete the whole circle, gives 

 a great part of its waters to the South Atlantic, and as a 

 proof of this it might be pointed out that the ice limit 

 does not approach the equator so much anywhere as it 

 does in the South Atlantic. 



The following facts may also be mentioned as in favour 

 of the hypothesis of a certain regular circulation taking 

 place in the manner described. A comparison of the air- 

 isotherms as well as the sea-isotherms both of the Atlantic 

 and Pacific Oceans shows that (i) the South Atlantic is 



colder than tnc North Atlan;..c ; (2) the Norih Atlantic is 

 warmer than the North Pacific ; (3) the South Pacific 

 is warmer than the South Atlantic. 



The higher temperature of the North Atlantic Ocean 

 has hitherto been generally explained by the influence of 

 the Gulf Stream. But a similar current exists in the 

 North Pacific, and yet this is colder. There is no doubt 

 that the Gulf Stream has a warming effect on some Euro- 

 pean coasts, but it is very probable that considering its 

 comparatively small breadth of about 100 nautical miles, 

 and shallow depth of only 100 fathoms, the stream is far 

 too insignificant to be able to exercise a perceptible influ- 

 ence upon the climate of the whole North Atlantic and of 

 the coasts surrounding this ocean. 



On the other hand it does not seem to have been suffi- 

 ciently appreciated hitherto, that a very large part of the 

 North Atlantic is filled by water, which has crossed the 

 equator, even if at a considerable depth. However 

 trifling the rise in the temperature of this water, as caused 

 by the passage over the equator, may be, when compared 

 to the general temperature of the South Atlantic, it is 

 nevertheless a fact that there is an important amount of 

 heat, which the South Atlantic loses and the North 

 Atlantic gains, on account of the very large extension of 

 the current. Nor can it be objected with regard to this, 

 that the mean temperature of that mass of water is pro- 

 bably below the mean temperature of air in the North 

 Atlantic, because there is no question of absolute heat, 

 but only of difference of temperatures between the North 

 and South Atlantic. 



The excess of water in the North Atlantic, which is not 

 carried back into the South Atlantic by the surface-cur- 

 rents, and which passes through the Arctic Ocean (where 

 it loses the heat it possessed) into the North Pacific, 

 causes a decrease of temperature in the latter, and, pro- 

 ceeding southward, i.e., again crossing the equator and 

 thus absorbing heat, produces an increase of temperature 

 in the South Pacific. Finally, the South Pacific gives 

 back to the South Atlantic a part of that water at a very 

 low temperature, which originally flowed from the latter 

 into the North Atlantic perceptibly heated, on account of 

 its passage through the tropics. 



This circulation, however, is not to be understood as if 

 the lowest strata of all the oceans took part in it j on 

 the contrary, there are doubtless only single currents in 

 the lower strata which follow it, while others may flow in 

 an opposite direction. Further observations will throw 

 light on these hypotheses ; those made up to the present 

 are yet insufficient and at times even contradictory. At 

 the same time it must not be overlooked that a constant 

 exchange of water between the lower and upper strata, 

 i.e., currents flowing in a vertical direction, are proved to 

 exist beyond doubt, particularly in certain zones. 



In conclusion Herr von Schleinitz considers the oceanic 

 system of currents to be evidently a very comphcated and 

 at present obscure one, upon which the observations made 

 on board the Challenger and the Gazelle throw but a very 

 faint light. 



The second part of the course pursued by the Gazelle, 

 as described above, did not differ sufficiently in latitude, 

 and therefore could not furnish any data which would 

 be useful or decisive on the subject in question. How- 

 ever, the observations which were made give results in 

 complete accordance with the hypothesis referred to 

 above. 



ON THE MEANS OF PROTECTION IN 

 FLOWERS AGAINST UNWELCOME VISITORS 



THE phenomena relating to this subject, which have 

 important bearings on the doctrine of selection, 

 have recently been discussed by M. Kerner in an interest- 

 ing monograph communicated to the Festschrift published 

 on occasion of the twenty-fifth anniversary of the Zoo- 



