DISCUSSION AND ANALYSIS OF WINDS. 



735 



SUNDA AND PHILIPPINE ISLANDS. 



In the seas south of Indo-China there is a double system of monsoons. The S. E. 

 trade crosses the equator in our summer, and gradually is changed to a S. and S. W. 

 wind, while during our winter the N. E. trade crosses into the southern hemisphere, 

 by and by assuming a direction from N. W. This last movement is caused by the 

 heating and rarefaction of the air over Australia. 



The Sunda Islands, being situated near the equator, are under the influence of 

 both monsoons. The one or the other of them can bring rain, and this depends 

 much more on local causes than on the situation north or south of the equator. 

 The direction of the wind in this Archipelago and the surrounding seas is not only 

 governed by the flow of air towards Asia and Australia (the great monsoons), but 

 also by the heating and rarefaction of the air on the islands themselves, especially 

 on the largest, Borneo and Sumatra. Even on the island of Java, narrow as it is, 

 there are great irregularities in the course of the monsoons caused by day and night 

 winds, at least at some seasons.^ 



I give here the mean direction of the winds at Batavia, from the elaborate dis- 

 cussion of the observations made at this place by Dr. Bergsma, director of the 

 Observatory. 







g 



t 







a 



i 







d 



a 







■g 



o^ 







"g 



oi; 







■^ 



oii 







d £ 









B £ 



|» 







«g 



.£3 

















03 ^ 















S 



K 







g 



« 







S 



fc 



January . . . 



N. 



87° W. 



.64 



May 



N. 



66° E. 



.28 



September . . . 



N. 



21° E. 



.23 



February . . . 



N. 



83 W. 



.61 



June 



N. 



60 E. 



.86 



October .... 



N. 



3 E. 



.02 



March .... 



N. 



27 W. 



.14 



July 



N. 



59 E. 



.35 



November . . . 



S. 



62 W. 



.25 



April .... 



N. 



85 E. 



.11 



August .... 



N. 



58 E. 



.29 



December . . . 



S. 



85 W. 



.74 



It will be seen that the west monsoon (in our winter) is much more regular than 

 the east monsoon. Besides, in the last season, the mean direction of the wind is 

 to the N. of E., while the S. E. trade should be expected. 



This is probably due to sea and land winds, which blow more regularly and 

 strongly, as this is a comparatively dry season. 



I give next some percentages from this region, adding the Philippine Islands, 

 where the extreme regularity of both monsoons is remarkable, while the Sunda 

 Islands show more local deflections. 





June to August. 



December to February. 1 



^ 





H 



73 



03 



m 



84 

 30 



10 

 3 



4 

 12 



4 

 10 

 7 

 3 

 4 

 10 



Is 



2 

 4 

 4 

 3 

 1 

 7 



8 

 33 



22 

 16 

 22 

 4 



65 



21 

 8 

 16 



8 

 12 



14 

 6 



12 

 6 

 4 



18 



W 



0! 



7 

 4 

 5 

 7 

 4 

 4 



M 





 4 

 4 

 3 

 8 

 3 





 6 

 9 

 12 

 14 

 13 





 8 

 13 

 18 

 15 

 33 



6 



17 

 26 

 21 

 25 

 14 



Zone 16. Santa Anna, Philippine Islands . . 





 3 

 5 

 2 

 2 

 3 





 6 

 5 



16 

 6 



19 





 7 

 15 

 36 

 30 

 33 



1 



10 

 38 



34 

 39 



9 



9 

 29 



16 

 2 

 14 



7 



" 19. Indian Ocean, 110°-H5° E 



" 19. Indian Ocean, 105°-110°E 



" 19. Southwestern Sumatra 



» An excellent sketch of the winds of Java, by Lieut. Jausen, is published in Maury's " Physical 

 Geography of the Sea." 



