BY T. GRIFFITH TAYLOR. 525 



A noticeable point is the way in which the isohyetal lines 

 bulge up the river valleys in many instances, from the dry 

 regions. (This is the wrong type of isohyetal bulge, from an 

 economic point of view, since it indicates a rainfall below the- 

 normal for the area in question. It may be termed a negative 

 loop). Thus in the stereo-isohyetal chart for 1900 (Plate xlvii.) 

 such bulges may be noticed in the 10-inch line up the Bogan 

 and Darling, and on the 20-inch line up the Namoi, Lachlan, etc- 

 In the similar chart for 1902 the phenomena are much more 

 marked (as in the cases of 10 and 15-inch lines on the Lachlan and 

 Murrumbidgee). 



We infer that river-valleys on the western slopes of the Main 

 Divide are relatively dry areas. The explanation is that the 

 " interfluvial " areas being usually elevated, cause the isohyetals 

 for the latter to become bulged towards dry areas, forming, 

 positive loops in these regions (i.e., in the right direction). 

 Thus arises the loop over the Warrumbungle Mountains (vide 

 Plate xlvii.) and, indirectly, the loops directed up the river 

 valleys previously cited. 



Paying particular attention to the stereo-isohyetal maps of the 

 Hunter River district, a very pronounced series of loops, pro- 

 jected towards the east, will be noticed in the charts for 1900 

 and 1902. These negative loops, concave towards the western dry 

 areas, indicate abnormal decrease in rainfall. Normally the 30- 

 inch line of rainfall would extend from x to Y direct (vide Plate 

 xlvii.); but, owing to the shifting of the divide by the Goulburn 

 and Hunter Rivers, the isohyetal 30-inch reaches almost to 

 Maitland. This indicates, as stated, a very much lower rainfall 

 than that of the districts north and south of the area. A similar 

 bulge is noted in the Peel River district which may be ascribed 

 to a like reason. In the chart for 1902 (in which year the rain- 

 fall was only half that of 1900) the corresponding loops in the 

 15- and 20-inch rainfall lines are very marked (vide R, s, t in 

 Plate xlviii.), though slightly further south. 



Finally may be mentioned the deflection of the anticyclones, so 

 often noticeable on the weather-charts, by the Blue Mountains. 



