After allowance had been made for orographical effects on the high 

 islands it was found that the frequency of months with a precipitation 

 effectiveness greater than 10 followed a distinctive pattern, as shown 

 on Map 1. There are no months with this precipitation effectiveness 

 along the dry tongue reaching from Bern (Gilbert Islands) to Christmas 

 Island, widening towards the east to include. Maiden Island. This tongue 

 is narrower than that postulated by Schott (1933) on the basis of rainfaU 

 alone. The belt of ocean with one to three months of precipitation effec- 

 tiveness over 10 is concentric to the dry tongue, including Nauru, Tohga- 

 reva (Penrhyn), and Pitcairn. This is approximately the area with less 

 than seven months of precipitation effectiveness over 6, as shown on 

 Map 2. Nauru and Ocean Island, however, have three months over 

 10 and seven months over 6, compared with Tongareva's and Pitcairn's 

 three and nine respectively. 



• There is little seasonal variation within the dry tongue. Maiden 

 reaches a precipitation effectiveness of 15-4 for the southern autumn 

 (Map 4) , falling to 6 • 1 in winter (Map 6) , to 2-4 in spring (Map 5) , and 

 rising again to 6 • 8 in summer (Map 3) . The other islands in the vicinity 

 show similar variations, and it may therefore be assumed that the dry 

 tongue does not change its latitude throughout the year, but rather 

 .shows a greater or smaller advance westwards. 



94 



