METEOROLOGICAL CONDITIONS. 23 



near Male island during the third week of February, 1900, wind 2 to 4 Admiralty scale, 

 regular never varying more than a point from north-east, depth 2 fathoms. 



Depth of Number Direction Current in miles per hour 



Position bottom in of Ob- of 



fathoms servations Current Greatest Least 



Passage Male to Hulule 24 ... 9 ... N. by W. ... 5-1 ... l-5> 



Wilingili 10 ... 9 ... S. by W. ... 5-3 ... 23 



Funadu 26 ... 9 ... W.N.W. ... 7-3 ... 31 



Two miles due N. of Male 28 ... 6 ... S.W.— W. ... 3-4 ... -8' 



Channel N. to S. Male. Atoll 245 ... 4 ... W. ... 4-1 ... 2-7 



I also sailed twice up to the passage between Hulule faro and Furenafuri, finding currents 

 of 3'7 and 21 knots into the lagoon. Of course all these currents were largely dependent 

 upon the tide, but it is a most noticeable feature that the direction remained constant in 

 spite of the latter, which hence only affected the rate. 



The depth, to which the currents of the Indian Ocean extend, has never, so fixr as 

 I am aware, been investigated. Yet in considering any theory of the formation of coral 

 I'eefs it is a most important factor, requiring consideration. I may perhaps refer to a 

 short paper by Admiral Sir W. Wharton on the " Foundations of Coral Atolls'-," where he 

 discusses in this connection the depth to which there may be motion sufficiently violent 

 to move material. 



I applied two methods of investigation to ascertain the directions of the currents, 

 i.e. by examining the specific gravity and temperature of the water at various depths, and 

 by means of a direction-indicator. Admiral Marakoff is the chief exponent of the first 

 method, which he used to examine the currents of the Bosphorus^ ; the direction of the 

 current is found purely by deduction''. I employed it in the channels round Male, men- 

 tioned above, but the differences were too small and variable for it alone to be a satisfactory 

 criterion. It was useful merely as a check on my second method. In the latter I at- 

 tempted to record the directions of the currents at any depth by means of a compass 

 (made for me by Messrs Negretti and Zambra). The latter was quite open to the water 

 at the side of its box, and could at any depth be jammed by a messenger. The whole 

 was placed in the middle of a V-shaped vane, which swung freely on a central bearing, 

 itself clamped on the sounding line. Immediately below the direction-indicator I placed 

 my current-meter, which I fitted to swing freely, and at the end of the rope I attached 

 a 20 lb. sounding lead. The compass gave uniform results, but the readings of the curi-ent- 

 meter varied so greatly that I omit any further reference to them. 



I carried out observations in the first place to ascertain, whether the currents were 

 the same at all depths in the deeper passages of atolls, as from theoretical considerations 

 I expected to find under-currents. I found as a result that there was no difference in 



1 Approximate ouly. I obtained my scale on the meter ^ I had the pleasure of discussing this subject with 

 by means of timed floats, using for the purpose corked Adm. Sir W. Wharton, Sir John Murray and Mr J. Y. 

 bottles, weighted with sand, with tiny flags, so that they Buchanan, before I left England. I am indebted to these 

 should not be affected by the wind. It must be checked gentlemen for much practical advice as to the work of the 

 frequently as the amount of friction may alter greatly. expedition. I am only sorry that I could not carry out their 

 Previously to this I had used the meter constantly in Miuikoi suggestions in their entirety. 



lagoon. ■> Vide " Le Vitiaz et I'Oc^an Paoifique." 



2 Nature, vol. lv. pp. 390—3, 1897. 



