HOUTMAN ABKOLHOS ISLANDS. 



147 



mean spring rise was nearer tbree than two feet. On both occasions when we 

 were at the islands the tides were diurnal, and it came as a surprise on our 

 first expedition to find that not only was there but one tide every 24 hours, 

 but that low water came at practically the same hour each day. On both 

 expeditions low water occurred always between 6 and 8 a.m. The harbour 

 master at Geraldton stated that during the summer months the tide at that 

 port was usually high about 9 p.m., with low water at 9 a.m., whilst in the 

 winter the converse was the case. Whether this be so or not at the Abrolhos 

 is impossible to say. We can only affirm that all our shore-collecting was 

 carried out in the early hours of the morning during the last week of 

 October and the month of November. 



Stokes gives the following rather surprising details which we can neither 

 confirm nor deny ; such conditions certainly did not prevail whilst we were at 

 the islands. The high-water at full moon and change occurred at 6 p.m. 

 During the night there was a short flood lasting six hours, the water rising 

 seven inches, and a shorter ebb of only two hours' duration, the tide falling 

 five inches. During the day, however, there was a flow of 8 hours 20 min., 

 and an ebb of 8 hours 5 min., the rise and fall being 25 and 26 inches 

 respectively. There Avere further variations at the different island groups. 

 It appears quite certain that the tides are very irregular. 



Rainfall. 

 No statistics exist, or are likely to exist in the future, concerning the 

 rainfall at the Abrolhos Islands. The nearest figures that can be utilised 

 are those for Geraldton, they will suffice to show the type of rainfall 

 experienced in this region. The rainfall is stated in "points,'' 100 points 

 equalling an inch. 











Rainfall at Geraldton. 













Year. 



Jan. 



Feb. 



Mar. 



April May June July Aug. 



Sept. 



Oct. 



Nov. 



Sec. 



Total. 



1913 .... 



30 



3 



17 



107 24 246 367 631 



268 



118 



7 



8 



1826' 



1914 .... 



3 



3 



Nil 



29 113 291 273 135 



5 



87 



93 



Nil 



1032 



1915 .... 



18 



459 



28 



78 241 790 529 332 



159 



97 



Nil 



18 



2749 



Averages for"! 

 the last 38 y 



16 



27 



33 



87 272 454 392 301 



135 



66 



25 



13 



1821 



years. J 





















Note.— The figures indicate " points," one hundred points of rain equal 1 inch. 



It will be seen that the average annual rainfall for the last 38 years is 

 18 inches. The dry months are October, November, December, January, 

 February, and March, the average fall recorded for this period of six months 

 being only 1*8 inches. 



