VI.—HUMIDITY AND WET BULB TEMPERATURES.
Except for the head stations, these records are not very numerous or reliable. An attempt has been made to collect the data for 1910; and the wet and dry bulb isotherms for midsummer (January) and midwinter (July) are shown in Figs. 53 and 54.
From the January isotherms, it will be noticed that in the hottest regions of Australia, the Pilbara Gold-fields, Western Australia, the humidity is by no means high.
The following table gives humidity figures for the hottest and coldest months at various stations. A comparison is interesting.
| Station. | Relative Humidities. | |
| January. | July. | |
| Nullagine | 35% | 50% |
| Broome | 71 l„ | 49 l„ |
| Cossack | 55 l„ | 59 l„ |
| Peak Hill | 29 l„ | 60 l„ |
| Coolgardie | 43 l„ | 72 l„ |
| Perth | 52 l„ | 78 l„ |
| Adelaide | 36 l„ | 76 l„ |
| Melbourne | 64 l„ | 80 l„ |
| Sydney | 70 l„ | 77 l„ |
| Brisbane | 66 l„ | 73 l„ |
From this it will be noted that the humidity reaches only 29 per cent. at Peak Hill and 35 per cent. in midsummer at Nullagine.
At Broome, further north and on the coast, the humidity is 71 per cent., and it increases to 78 per cent. at Port Darwin in January. All down the east coast the heavy rainfall leads to much greater humidity than on the west coast. But, as the rainfall decreases rapidly towards the interior, the region with humidities over 70 per cent. in midsummer is very narrow.
In the chart showing the wet and dry bulb isotherms for July (see Fig. 54) the north of Australia at this time is experiencing the dry season, so that high humidities can only occur in the south. Since the average dry bulb temperature in the southern moiety is only about 50 F., none of these humidities though well above 80 per cent. in places have any deleterious effect on health.
Humidity data for the six capital cities are given in the following paragraph, together with graph relating to the monthly humidity and temperature:
- (1) Perth.—At Perth the mean annual humidity at 9 a.m. is 62; the greatest monthly mean is 83, and is in June; and the lowest, 42, in January.
- (2) Adelaide.—At Adelaide the mean annual humidity at 9 a.m. is only 56; the mean monthly humidity has been as low as 33 in January and December, and as high as 94 in June.
- (3) Brisbane.—In Brisbane the mean annual humidity at 9 a.m. is 68; the lowest monthly mean recorded is 47, and is in September; and the highest, 85, in the months of March and May.
- (4) Sydney.—In Sydney the mean annual humidity at 9 a.m. is 73, the greatest monthly average, which occurred in May, 1891, was 90; whilst the lowest monthly mean, 52, occurred in the month of December, 1911.
