34 



NA rURE 



{_Nov. 



1886 



Challenger on her voyage from Hawaii to Tahiti. Her 

 observations were illustrated by two diagrams, one show- 

 ing the direction of the current, and the other the dis- 

 tribution of temperature and density in the upper layers 

 of the water traversed. The easterly current was found 

 between the parallels of 5" N. and 10" N., there being two 

 streaks of maximum velocity, one between 7' and 8' N., 

 and the other between 9' and 10°. In the former the 

 mean daily set was 54 miles ; in the latter it was probably 

 quite as high, but it could not be accurately determined, 

 as the ship passed from westerly to easterly current in?the 

 course of the 24 hours, and the observed current of 20 

 miles represented the difference of the two. The streaks 

 pr axes of strong easterly current are sharply defined by 

 areas of abnormally low surface density. The whole of 

 the area of easterly-running water has a comparatively 

 low density, but where there is a sudden acceleration 

 of its velocity, there is a correspondingly sudden drop in 

 its density, so that the existence of a strong easterly cur- 

 rent in equatorial regions maybe guessed with great proba- 

 bility by the use of the hydrometer. The diagram showed 

 also in a very marked way the protective action of the 

 fresh surface water in preventing the penetration of heat 

 into the lower layers of the water. A temperature of 

 60' Fahrenheit is found here at a depth of 50 fathoms 

 from the surface, while in the westerly-running current, a 

 little further south, the same temperature occurs at a 

 depth of over 100 fathoms. In this region there are great 

 inequalities in the density of layers of water at the same 

 depth and within a short distance of each other. Thus, if 

 the column of water between 20 fathoms and 70 fathoms 

 from the surface be considered, its weight at the station 

 where the westerly-running equatorial current prevails is 

 only 88 per cent, of its weight under the counter equatorial 

 current, the distance between them being not more than 

 200 miles. This disturbance of statical equiUbrium must 

 be balanced by circulation of water between the localities, 

 and hence the violent and conflicting currents observed in 

 these regions. The study of the currents of equatorial 

 regions would well repay the trouble of the investigation. 

 The counter equatorial current is particularly interesting, 

 and its dynamics obscure. Its range is very super- 

 ficial, and its physical conditions can be studied without 

 theelaborate and costly equipment required for the research 

 of oceanic depths. 



To the north and to the south of the equatorial 

 bights of the western shores of Africa and America 

 we have a remarkable similarity in the distribution of 

 temperature in the coast waters. The transition from 

 equatorial heat to extratropical cold is very marked : 

 on the North American shore, at Cape St. Lucas, the 

 southern extremity of the Californian peninsula ; on the 

 North African, at Cape Verd ; on the South American 

 shore, at Cape Blanco ; and on the South African, at 

 Cape Frio. In rounding Cape St. Lucas the temperature 

 was observed to fall from 75° to 65' F. in less than an hour ; 

 and a similar difference of temperature was found in 

 rounding Cape Blanco between Payta and the Guayaquil 

 river. On the Morocco coast the water is found to have 

 a temperature quite 10' lower than is found twenty miles 

 to sea. These sharp transitions are found only close in- 

 shore, and they have usually been attributed to surface 

 currents from higher latitudes. This explanation is at 

 variance with the observations of navigators on the coasts, 

 who do not notice any currents which would be strong 

 enough to bring water many hundreds of miles under a 

 burning sun without sensible rise in temperature. The 

 occurrence of these coast areas of abnormally cold water 

 is explained when we recognise that they are the wind- 

 ward shores of the oceans. The trade winds blow from 

 them towards the equator, and in doing so mechanically 

 remove water, which has to be supplied from the readiest 

 source. This source is the deep water lying off the conti- 

 nental coasts, which is supplied by a gradual drift of cold 



water from high latitudes. Hence, though the low tem- 

 perature of the coast waters referred to is due to the cold 

 of high latitudes, it is not supplied by a long coast Polar 

 current, but by a short vertical one. This view was very 

 strongly supported not only by the temperature of the 

 water, but by its other characteristics, especially colour. 

 The outside ocean water is of an intense ultramarine blue ; 

 the coast water off Mogador had the clear olive-green 

 colour met with constantly in Antarctic seas. The same 

 is observed on the west coast of North and South America,, 

 and it would be of the highest interest to have these waters 

 investigated from a biological point of view. No waters 

 in the ocean so teem with life as those on the west coast 

 of South America. A bucket of water collected over the 

 side is turbid with living organisms, the food of countless 

 shoals of fish, who, in their turn, afford prey for innumer- 

 able schools of porpoises. One remarkable school which 

 accompanied the ship for some time consisted entirely of 

 females, each accompanied by a calf following in her wake 

 and mimicking her every movement. Along with abund- 

 ance of life this coast unites facilities for investigating it. 

 At every port there are plenty of shore boats anxious for a 

 fare, and with a tow-net and a few bottles a naturalist 

 might make a rich collection of the shore-water fauna of 

 the coast in one trip from Valparaiso to Panama. 



The most remarkable confirmation of the view that 

 the cold water on the windward shores is due to- 

 a submarine source has been quite recently supplied 

 by the observations of Capt. Hoffmann, of the German 

 man-of-war Mowe, on a voyage from Zanzibar to 

 Aden. He kept close to the coast as far as possible, 

 and observed a very uniform surface temperature of 

 78' to 80° F. from Zanzibar to Cape Warschek, when it 

 iDegan to fall, and remained at a temperature of from 60" 

 to 65° F., until Cape Guardafui was reached, when the 

 temperature went up rapidly to 86'. The minimum tem- 

 perature observed was 59° F., and Capt. Hoffmann calls 

 particular attention to the dark-green colour of the water, 

 and in speaking of its low temperature he recognises that 

 its source can only be the deep water in the neighbour- 

 hood, as the surface water on both sides has a temperature 

 bordering on So' F. The Mouie passed through these 

 seas in the month of July, when the south-west monsooii 

 is blowing most strongly, and at this season the Somali 

 coast is a pronounced windward shore, and exhibits the 

 same characteristics as the windward shores of Morocccv 

 or South America. The coral growths, too, which are scv 

 abundant north and south of it are here quite absent, 

 thus accentuating the eastern or windward character of 

 the shore. 



NOTES 



The following is the list of selected names to be submittedl 

 to the Fellows of the Royal Society at the forthcoming anni- 

 versary meeting (November 30) for election into the Council 

 for the ensuing session : — President : Prof. George Gabriel 

 Stokes, M.A., D.C.L., LL.D. ; Treasurer: John Evans, 

 D.C.L., LL.D.; Secretaries: Prof. Michael Foster, M.A., 

 M.D., Lord R.iyieigh, M.A., D.C.L. ; Foreign Secretary r 

 Prof Alexander William Williamsin, LL.D. ; other Members- 

 of the Council : Prof Robert B. Clifton, M.A., Prof. George 

 Howard Darwin, M.A., LL.D., W. T. Thiselton Dyer, M.A-, 

 Prof. David Ferrier, M.A., Edward Franklantl, D.C.L., 

 Arthur Gamgee, M.D., Archibald Geikie, LL.D., Prof. Joseph 

 Henry Gilbert, M.A., John Hopkinson, M.A., D.Sc, J. 

 Norman Lockyer, F.R.A.S., Sir Lyon Playfair, K.C.B., 

 LL.D., Prof. Bartholomew Price, M.A., Prof. Pritchard, 

 M.A., Admiral Sir George Henry Richards, K.C.B., Prof. 

 Arthur Schuster, Ph.D., Philip Lutley Sclater, M.A., Ph.D. 



In the third volume of Ray's " Historia Planlarum " there is 

 a list of plants collected in the Island of Luzon by George Joseph 



