Modifying Climate. \\9 



mean annual rainfall for the three successive decades for Swam 

 Hill, Tyrrell Downs, Waitchie, and Murray Downs, are 15.6 

 in., 10.9 in., and 11.9 in., giving A, .69 A, and .76 A. 



Creation of Water Surfaces. 



It is perhaps not possible to store wafer in sucH amounts- 

 inland, as to distinctly increase the general humidity of the at- 

 mosphere, but " every little helps." It is possible that the rain- 

 fall averages along the shores of some of our land piercing inlets- 

 may be indicative of future possibilities. There are two very 

 suitable for examination — Spencer's Gulf and Port Phillip Bay,, 

 and it fortunately happens that the shores of both are fairly 

 well lined with rainfall stations. 



The length of Spencer's Gulf is great compared with even 

 its greatest width, hence winds bearing rains from the open ocean 

 are confined to a small angle, and this is so nearly due south 

 that but little rain could be brought in from that direction. Ex- 

 cept near the entrance, where elevated land just inland from 

 stations on the western shores of the Gulf gives these an increased 

 rainfall, the western stations have a distinctly lower rainfall than 

 the eastern ones. This difference appears to be about 2\ inches 

 50 miles from the entrance, where the Gulf has a width of about 

 70 miles, and slowly increases to 3 inches as far north at Pt. 

 Broughton, where the distance from the entrance is about 130 

 miles, and the width 32 miles. Thence it diminishes to zero at 

 the head of Port Augusta. 



If Spencer's Gulf were silted up, it would be incredible that 

 the rainfall on the resulting low level plain, especially in its 

 northern portion, should be superior to that of, say, Yardea or 

 Nonning, which stand on plateux of about 1000 feet in eleva- 

 tion to westward. As the average rainfalls of these stations 

 are only about 10 inches, the rainfall near the head of the Gulf 

 should almost certainly be less, say, about 8 inches. This would 

 make the narrow strip of water forming the northern part of 

 the Gulf responsible for an increase of 3 to 4 inches on the 

 western shore, and 5 or 6 inches on the eastern. 



For the sake of more definiteness as to the effect of evapora- 

 tion from the waters at the head of the Gulf in increasing the 

 rainfall, I have analysed the rainfalls at four of the stations with 

 regard to the chief wind directions. The stations are Port Pirie 

 and Hummock's Hill, Pt. Lowly and Germein. These form 

 opposing pairs. Between Pt. Pirie and Hummock's Hill the 



