METEOROLOGICAL CONDITIONS. 25 



I have in Fig. 5 represented the reef in its low-tide condition, when it is practically 

 awash. Undoubtedly the surfiice current to some extent would be accentuated, and pass 

 over the reef at high tide. It would be checked, however, by its friction on the reef, so 

 that it would not probably gain greatly in strength, and hence the additional amount of 

 water passing over any reef would be relatively small. In Minikoi during four nights, 

 when I was anchored close to the reef, I never recorded a greater current than 24 knots 

 per hour, although taking observations every hour. The backwash outside the reef, which 

 appeared to be strongest close to the bottom, is of interest, as it might well carry out 

 any coral or nullipore detritus from the reef and be the chief agent in extending its 

 foundations further and further seaward. The depth, 20 to 60 fathoms, where the steep 

 slope commences off most oceanic reefs, may well be the critical point for the oceanic 

 currents off those reefs. Speculation is, however, premature until these observations have 

 been confirmed, and more exact results have been obtained. 



Tides are of course at all times largely influenced by the prevailing winds and 

 currents; they are hence very irregular in the Maldives and Laccadives. At Minikoi I found 

 a rise of about o feet 9 inches at springs and .3 feet 6 inches at neaps; at Addu the 

 rise is only about 4^ feet at springs. In the south-west monsoon the flood commences 

 extremely slowly, rises rapidly, and as slowly attains its maximum, at which it may hang 

 for some time ; the ebb, when it has once commenced, is more regular. In the north-east 

 monsoon both flood and ebb pursue an even course. The flood always apjiears to set to 

 the east and the ebb to the west. The latter at Minikoi in the south-west monsoon is 

 almost invariably the longer in the proportion of about seven to five. There is, however, 

 very considerable variation in accordance with the strength of the winds, and I have even 

 observed the above proportion almost reversed ; further it alters with the time of high 

 water. The monsoon winds commonly moderate after the heat of the day during the night. 

 Hence in the south-west monsoon the obstruction they form to the fall of the tide is not 

 so great as in the daytime, with the result that the lowest tides occur in the early 

 morning (high water, full and change, in the lagoon at Minikoi being about 10 h. 30 m.). 

 In the north-east monsoon the winds assist the falling day-tide, and the evening tides are 

 hence the lowest. This, however, is in no sense a complete explanation, as during dead- 

 calm weather in the Maldives with no appreciable oceanic current I found that the same 

 phenomena are nearly as strongly marked. The difference between the rise and fall of the 

 morning and evening tides at springs is often in heavy weather as much as 2 to 2| feet. 

 On one occasion towards the north of the atoll of Minikoi the morning tide rose 7 feet 

 5 inches, while the evening tide did not show more than 4 feet 7 inches ; it was blowing 

 at the time a gale from the south-west. 



The rainfall varies, increasing from the north to the south of the groups. At Minikoi 

 its total is about 100 inches per annum, the greater part of which falls during the first 

 month of the south-west monsoon. During the rest of the year, especially in December, 

 heavy showers of short duration are not infrequent. Vegetation increases in luxuriance from 

 north to south in the Maldives. At Addu there is no dry season, and the fall probably 

 reaches a total of about 150 inches. 



The temperature in the shade varies generally between 70" and 90° F., both day and 

 night. For ten days at the end of February, 1900, it did not fall below 85° either by 

 G. 4 



