Modifying Climate. ] 2 1 



The results are very interesting. Comparing Port Pirie and 

 Hummock's Hill we see that as regards winds from the western 

 "half-circle, half the total rain at Port Pirie comes with winds 

 :from between N. and W.S.W., and for these the average gain 

 per annum over Hummock's Hill is 1-J inches, the rainfall being 

 .apparently increased by that amount and almost doubled by 

 moisture taken up from a 20-mile stretch of water. The same 

 proportion holds for the westerlies in general, which give 318 

 points to Hummock's Hill, and 640 to Port Pirie. 



Now, taking the winds with easterly components, the gain to 

 Hummock's Hill over Port Pirie is nearly as substantial, the 

 Port Pirie rainfall of 3^ inches under easterly winds being raised 

 to 5 inches from the moisture picked up in the passage over 

 the water. This is perhaps even more than one would have ex- 

 pected as in some instances the rain clouds would be moving in 

 a different direction from the surface winds, and would carry 

 "back to Port Pirie some of the added moisture. 



Similar results are to be obtained from other comparisons. 

 T or example, taking Point Lowly and Port Germein ; for winds 

 between N. and W.S.W. — these not traversing the greater areas 

 of the Gulf — the relative gain to Port Germein is 0.58 inch, and 

 for easterlies, the relative gain to ' Pt. Lowly is 0.77, which is 

 ■quite as much as one would expect considering the nearness of 

 the two stations, and the way Pt. Lowly projects into the Gulf, 

 enabling it to gain not only from easterly winds, but at times 

 from northerly or even west-south-westerly winds. 



It would thus appear that out of the ten inches of Port Pirie's 

 irainfall under definite wind direction, at least 3^ inches come 

 from the adjacent waters, and if the same proportion holds for 

 the indeterminate portion, the total gain will be at least 4-J inches. 

 Hence, if the Gulf were silted up, its annual rainfall would 

 not exceed 9 inches, and would probably be less, thus bearing 

 out the previous more generally derived opinion. 



The rainfall data from Port Phillip Bay are equally striking, 

 .stations on the Eastern shores receiving up to ten inches more 

 than Western stations in the same latitude. 



It is hardly necessary to remark that it is in rainy weather 

 the principal additions to the rainfall must be made by local 

 •evaporation. Under generally anticyclonic conditions, as in some 

 of our great drought years, the rains must largely fail ; but the 

 value of the increased amount in more favourable years is not 

 thereby lessened. 



