- (5) Melbourne.—The mean annual humidity derived from the 9 a.m., 3 p.m., and 9 p.m. observations in Melbourne is 71; the greatest monthly average, 88, in June and July, 1858; and the lowest, 49, in December, 1908.
- (6) Hobart.—Hobart's mean annual humidity at 9 a.m. is 71; the highest monthly mean, 92, in June; and the lowest, 51, in February and December.
From the above results it is seen that in respect to relative humidity, Sydney has the first place, while Hobart, Melbourne, Brisbane, Perth, and Adelaide follow in the order stated, Adelaide being the driest. The graphs shown on Fig. 55 show the annual variations in humidity. It will be observed that the relative humidity is ordinarily, but not invariably, great when the temperature is low.
N.B.—For the thin lines (relative humidities), the degree numbers represent the percentages of possible saturation.
VII.—SPECIAL FACTORS CONTROLLING CLIMATE.
Before considering the vital question of rainfall, which our study of temperature and barometric changes now enables us to do, it may be well to glance at two factors of considerable importance in this connexion.
Ocean Currents certainly affect the coastal climates to a great extent, while the topography practically determines the local deviations from the general simple curves of the isohyets around the heart of the continent.
Ocean Currents.
Sub-dividing the coast into six regions, as in the case of the winds, and comparing the charts issued for the U.S.A. and British pilots, we get a fair idea of the variability of the currents in some of these regions.
Northern Coasts.—A fairly constant flow from east to west characterizes the winter (April, May, June, July, and August). It will not affect the climate of Northern Australia appreciably. During the rest of the year east and west currents seem both to occur in coastal waters.
Queensland Coast.—During winter and spring (May-October), there is a fairly permanent set to the south-east. This brings warmer waters in temperate regions. During summer streams seem to show a tendency to flow north-westward along the Barrier Reefs.
New South Wales Coast.—Generally a flow to the southward, but varying especially in midwinter. This has a tendency to warm the coast lands.
South Australian Coast.—A very general westerly drift, but in the Bight the streams vary considerably, especially in Autumn (February-June). There is a southern component in this current, so that the result is to cool the southern shores of Australia.
South-west Coast.—A fairly steady current from the south-west most of the year. In winter it appears less constant, and during April-July eddies near the coast, and exhibits a movement to the south. This is a definitely cool current on the whole.
North-west Coast.—The same condition as along the south-west coast; hence a cold-water current occurs, but not so important as further south.
