X.NXIV. 
ChARLKS AuyTTX (tARDNER, 
3. HUMIDITY, EVAPORATION, AXD WIND. 
There are but 36 stations in Western Australia from which data are 
l>ublished concerning temperature and humidity, and these are (jviite in- 
adequate for tlie purpose of constructing a map. The appended tables have 
been compiled for reference and the forming of general conclusions, and contain 
all the information which has been officially published. 
While the 9*0 a.m. readings for re^lative humidity may be regarded as. 
typical for the 24:-hour period in certain coastal areas, it \\'ill be at once aj)- 
parent that this is not so for the inland stations ; the relative humidity tables 
of monthly mean percentages illustrate this point quite clearly. They exhibit 
the fact that in the wet forest areas, the range between morning and afternoon 
(9*0 a.m. and 3-0 p.m.) readings is very slight, while in the sclerophyllous. 
woodland formations it is high, e.tj., while at Cape Leeuwin this figure does 
not exceed 7 per cent., in inland localities it is as high as 24 j)(‘r cent.. 
Another point that has to be considered is that the 9*0 a.m. leadings taken 
in summer, when in the south the sun rises at 4-30 a.m., are quite a different 
(juantity from those taken in winter, when the sun rises at 7-0 a.m. It is- 
interesting to compare the relative humidity figures for Kellerberrin and 
Perth with those of Carnamah and Mundiwindi, all of v4iich have different 
climates. The table of relative liumidity for the four consecutive driest 
months is also instructive, and emjdiasises still more the climatic extremes, 
of the inland stations. 
Information regarding ovafjoration can be obtained from the figures given 
for the saturation deficit and the Meyer Ratio. There are only four official 
evaporimeters in Western Australia, the most inland of which is at Merredin. 
One at Wiluna or Mundiwindi would be of much value. The following tabl& 
gives the monthly evaporation 
in inches 
for the four 
stations 
- 
Perth. 
Narrogin. 
Chapman. 
Merredin. 
January 
10-370 
9-083 
1 1 - 940 
13-151 
February 
8-650 
7-570 
10-192 
1 0 • 860 
March 
7-550 
6-433 
9-226 
9-359 
April 
4 • 670 
3-780 
6-792 
5-979 
May 
4-670 
2-361 
4-160 
3-641 
June .... 
1-770 
1 -609 
2-629 
2-289 
July 
1 -730 
1 624 
2-473 
2 - 09 a 
August 
2-360 
1 -864 
2-942 
2-611 
September .... 
3-410 
2-513 
4-055 
4 - 010 ' 
October 
5-340 
3-833 
6-431 
6-527 
November .... 
7 ■ 660 
6-156 
8-951 
9-764 
December 
9-780 
8-505 
11 -391 
12-285 
Total 
65-070 
55-331 
81-162 
82-557 
4. RATIO OF PRECIPITATION TO EVAPORATION. 
AVliile heat and moisture are the most important of the elements of the 
climate affecting plant life, water is of importance to the plant in tvs o ways : 
as soil water, and as atmospheric moisture. The relative humidity depends, 
upon the temperature of the air and the water vapour present ; the hotter 
the air, the more water vapour it can hold, and the relation of the temperature 
of the air to its water vapour content controls the loss of water from the aerial 
j)arts of the plant. Vegetation is therefore dependent upon precij^itation 
and evaporation. 
