Any information with regard to the humidity of the atmosphere, also, will he of great value. All physicians are of opinion that a high temperature, combined with moisture, is very irritating to the lungs of those affected with pulmonary disease.
Before setting forth the different answers in response to this, it will be desirable to refer briefly to the term "humidity." The humidity of the atmosphere is defined as the degree of its approach to saturation. Air completely saturated is represented by 100, and that absolutely free of vapour by 0. As a matter of fact, however, the latter never occurs; even in the driest regions of Arabia a humidity of 10 per cent. is almost unknown. For its estimation the Wet and Dry Bulb thermometers are employed. These consist of two ordinary thermometers. One has its bulb exposed so as to register the temperature of the air. The bulb of the other is covered with muslin; this latter material being kept wet through its connection with a cotton wick dipping into a vessel of water. The water ascends from this vessel by capillary attraction, spreads over the muslin, and evaporates quickly or slowly, according to the dryness or moistness of the atmosphere. Thus when the air is driest the difference between the two thermometers will be greatest, and, on the contrary, when it is completely saturated with moisture the two readings will be almost identical.
A considerable part of the colony, forming the western plains, is subject to great heat, caused, no doubt, by the sun's great power on treeless plains, and the almost total absence of cooling winds; yet, although in summer the temperature here frequently rises over 100°, and sometimes up to 120°, owing to the cold at night and in winter the mean temperatures are not greater than those of corresponding latitudes in the northern hemisphere. This region of the colony is remarkably dry, and stock of all kinds thrive well and are very free from disease. At Bourke, the driest place in the colony, the humidity for a long series of years is - in the spring 54°, in the summer 49°, in the autumn 61°, and in the winter 74°. At Sydney the humidity in the spring is 69°, in the summer 70°, in the autumn 79°, and in the winter 79°.
The humidity of the air of Melbourne is low, the average being 71 per cent. In the summer it falls to (55, and on hot days is generally very low. The characteristic of our hot weather is that it is usually extremely dry; the exceptions are very few, and occur in the late spring and early autumn during thundery, muggy weather. On the hottest days, with north winds, the dryness makes the heat much more endurable, and the humidity frequently falls to between 30 and 40 per cent.
Attention has already been drawn to the fact that the hot, dry air met with on the Adelaide plains is far more endurable than a lower temperature in which the atmosphere is surcharged with aqueous vapour.
A damp atmosphere is a rare thing in South Australia during the summer, though in March there are at times some warm and humid days. In the winter the air for the most part is dry, although the nights are often damp. The Mount Lofty ranges, close to Adelaide, afford a cool retreat; they have a very large rainfall, in some years over 50 inches. The climate at Mount Gambier, in the south-eastern part of the colony, is cooler and damper; it has also a much heavier rainfall than the Adelaide plains.
Of what duration are the different seasons, and to what months would you apportion each season?
Spring - September, October, November; Summer - December, January, February; Autumn - March, April, May; Winter - June, July, August.
Spring - September, October; Summer comprises the five months from November to March inclusive; Autumn - April, May; Winter - June, July, August. Practically, in South Australia the year may be divided into two seasons, namely, Spring, the seven months from April to October inclusive; and Summer, the five months from November to March inclusive.
With regard to Southern Queensland, the seasons may be provisionally apportioned as follows : Spring - August, September, October; Summer - November, December, January, February; Autumn - March, April, May; Winter - June, July.