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a dependency of the Circular Head Company (Van Diemen's Land), 2700 feet above the sea, the fall of rain is less than on the Hampshire Hills, which average 1800 feet above the sea; the rich arborescent vegetation which is found on the latter, and the partial barrenness of the former, thus differently influencing the condensation of the floating vapours.
The influence of that vegetation upon the amount of rain is still better exemplified by a comparison of the registers of the two stations of the Van Diemen's Land Company. Thus, at Circular Head, a neck of land which projects into the sea, clear of timber, and under cultivation, it rains less than at Woolnorth, also on the sea coast, and equally exposed to the north, but surrounded by a thick forest of luxurious growth.
Other particulars, extracted from the registers, and relating to rain, may be embraced in the following remarks.
The greatest fall of rain recorded in New South Wales, during twenty-four hours, amounted to twentyfive inches, (Port Jackson). On the western side of the dividing range, however, (Namoy River,) marks of extraordinary floods are found; floating bodies, such as grass, rushes, dried branches and bushes remaining attached to the trees at the prodigious height of ten feet from the ground.
The temperature of the rain, as observed in Van Diemen's Land, is sometimes above and sometimes below that of the ambient air. Thus it appears, from the register, that rain has fallen while the thermometer has been below the freezing point; and also when the dry themometer has indicated a temperature of 75°, and the wet one 68°; the temperature of both receding to 60° after such fall of rain.
The periods of the year when the maximum of rain falls, present, in their monthly and seasonal
means, some differences, which as yet cannot be satisfactorily accounted for: thus, the maximum of rain at Port Macquarie takes place during the summer season; while at Port Jackson, Port Philip, Woolnorth, and Circular Head, it occurs during the winter months. Port Arthur, again, which is the southern extremity of Van Diemen's Land, had its maximum for 1838, 1839, 1840, in the summer season; while the maximum for 1841 and 1842 occurred in winter. Its averages, as shown in the above table, render the quantities of each season nearly equal.
The registers moreover exhibit a very remarkable fact, viz., that New South Wales is more plentifully supplied with rain than Van Diemen's Land; the table of averages showing that the annual quantity in the former colony exceeds that in the latter by eight inches. However, owing to its more gradual condensation, the lesser quantity of rain in Van Diemen's Land is a more valuable and beneficial concomitant of the climate than the greater quantity in New South Wales.
As compared with other countries we may now see that, notwithstanding the general outcry about the dryness of their respective climes, New South Wales and Van Diemen's Land are better provided with rain than even England: thus London *, generally noted for its wet climate, has an annual quantity of rain equal to 22*19 inches; while the average which falls upon the surface of a station in New South Wales is 48 inches, and in the sister colony 41 inches, per annum.
The evaporating gauge, alluded to under the head of winds and currents, was registered at Port Stephen by Captain P. P. King, and at Launceston by the writer, at nine A. M., at noon, and at three P. M., together with the barometer, thermometer, and psychrometer, and the winds and currents. It was kept isolated on a small stand in the open air, and sheltered from rain and sun. Besides its additional evidences relating to the hot wind, it has furnished other results bearing upon meteorological questions. The most remarkable are, that, under ordinary circumstances, the amount of evaporation in Port Stephen, for any of the six hours included between nine A. M. and three p. M., corresponds with that in Launceston; but, for the eighteen hours between three P. M. and nine A. M., it differs, the evaporation in Port Stephen in this case exceeding, on an average, that of Launceston by one hundredth part of an inch.
* Daniell's Essay on the Climate of London.
The season of the maximum evaporation is summer, that of the minimum is winter. In both seasons, the daily evaporation is greater between noon and three P. M. than between nine A. M. and noon.
Under ordinary circumstances, the evaporation during three hours, whether it be before or after noon, does not exceed 00'070; when, however, the hot wind blows, its amount in Port Stephen reaches 00-120, while in Launceston it is but 00'081 of an inch.
The absolute amount of monthly and annual evaporation in the gauge, expressed in English inches, was as follows: —
The difference of evaporation between the two localities, separated by 6° 20' of latitude, amount then to about 2'89 of an inch.
The examination of the register of evaporation and of the hygrometrical state of the atmosphere does not lead to the disclosure of any connection existing between the two phenomena.
The following table shows the extraordinary variation of the rates of the tension of vapours, from which nevertheless uniform quantities of water evaporated.
TENSION OP THE AQUEOUS VAPOUR IN THE ATMOSPHERE, AS
Thus, as illustrated in the above table, at -433 of tension of vapour, the. evaporating gauge indicated during the space of three hours, at times no evapora
tion, at times amounts equal 00-010, 00-020, 00-030, and 00-040.
Again, at *513 of tension, the maximum of evaporation took place; and at -508, and -537, the minimum. Furthermore, in the averages of the rates of tension, no relation to evaporation is perceptible; the numerical means of -480 and -470 corresponding to 00-020 and 00-070 of the evaporated quantity of water.
The registered temperature, during the process of evaporation, shows, as may be seen in the following tabular form, that it has no more relation to evaporation than the tension of the aqueous vapour had.