i ie 2 a 
TRANSACTIONS OF THE SECTIONS. 5F. 
range for the same time, or the difference between the highest and 
lowest altitude of the barometer, was found to be 2°821 inches. The 
fluctuations or deviations from the mean state are greatest in December 
and smallest in August. The mean temperature of Perth, derived 
from the maxima and minima of each day, according to observations 
continued from the beginning of 1829 to the end of 1834 inclusive, is 
48°14. The mean obtained from the annual means, by observations 
taken at nine o'clock in the morning, and half-past eight in the even- 
ing, is 47°9; and the mean of the annual extremes, derived from the 
greatest heat and greatest cold, for each year, is 48°25. Lastly, the 
mean of the highest and lowest temperature for the entire period of 
years is 47°-5. By a comparison of the mean temperature of the seve- 
ral months, it appears, that in different years the month of July pos- 
sesses the greatest uniformity of temperature, and the month of January 
the least. The temperature of March, April and May, especially that 
belonging to the last of these months, has a considerable range in dif- 
ferent seasons, on account of the variable winds in spring; and the 
temperature of August and September seems to be still more fluctua- 
ting, a circumstance that occasions the late and early harvests, which 
happen in different years. The lowest temperature, within the period 
to which the above observations refer, occurred on the 26th of Decem- 
ber, 1830, when the instrument stood at 16°, and the greatest heat 
took place on the 28th of July of the same year, when the thermome- 
ter was at 79°. The greatest annual range for that year was therefore 
63°; but the mean annual range for the entire period was only 57°5. 
The most abrupt change of temperature occurs between the middle of 
October and the middle of November, and to this must probably be 
ascribed the increase of pulmonary complaints, which takes place at 
that gloomy and disagreeable season. 
The mean hygrometric state of the air at Perth, is when the atmosphere 
is charged with about four-fifths of the entire quantity of moisture it is 
capable of holding in the state of vapour at the mean temperature. The 
dew-point, which corresponds almost exactly with the minimum tempe- 
rature, in the case of the different months, is depressed about 6° or 7° 
below the mean temperature in winter, and about 8° or 9° below it in 
summer. The month of April possesses the smallest relative humidity, 
and the month of November the greatest; the former month being, in the 
ordinary acceptation of the term, the driest, and the latter the dampest 
month of the year. The mean quantity of rain which falls at Perth, de- 
rived from a period of six consecutive years, viz. from the beginning of 
1829 to the close of 1834, is 30°89 inches. The greatest anomalies, 
with respect to the quantity of rain which falls in different seasons, hap- 
pen in July, in which month the difference between the greatest and 
least quantity is 4°65 inches ; and the smallest occur in November, when 
the difference is only *$1 inch. The maximum quantity of rain for a 
period of sixteen years is 31-01 in., and the minimum quantity 15-59 in. 
The annual number of fine days, deduced from a period of six conse- 
cutive years, is 253 ; and the number of days on which there was either 
rain or snow, 112; the former being more than double of the latier. - 
