417 
1887.] Mr A. Rankine on the Thermal Windrose. 
temperatures in certain months, which difference is obviously due 
to the inequality of the frequency of the different winds. 
As the character and relative frequency of each wind have 
already been discussed by Mr Omond, it only remains to add a few 
words regarding wind-temperature, as far as the accompanying table 
sheds any light on the subject. 
The first point to be noticed is, that on the mean of the year the 
south is the warmest wind, its temperature being 3 2° "6 ; and the 
north-east is the coldest wind, its temperature being 26 ° '5 ; and 
also that the winds in their order of highest temperature are — S., 
S.W., W. (N.W. = S.E.), E., 1ST., N.E., — the north-west and south- 
east winds being equal in temperature, and the east and north winds 
almost so. In each of the seasons the north-east wind is the coldest, 
and, with one exception, the south is the warmest, the exception 
being winter, when the warmest wind is the south-west. An 
inspection of the results for the different months shows that the 
above order of highest temperature of the directions varies consider- 
ably from month to month, as does also the difference between the 
temperatures of the warmest and coldest winds in each month, the 
maximum difference being 10° *7 in March, and the minimum 
4 0- 2 in April ; while the mean of all the monthly differences is 6° *7. 
This difference on the mean of the seasons is greater in winter 
and spring than in summer and autumn, being least in summer. 
Though the means for the year and for the seasons show that the 
warmest and coldest points are almost constant, yet the monthly 
results show that these points oscillate, the warmest point 
markedly and the coldest rather less so. During the winter 
months the warmest point is south-west, but, as the year advances, 
it swings round through south to south-east, which is its direction 
in July and September. The coldest point is north-east for nine 
months ; and though in February it is south-east, in June east, and 
in November north, it has not so well defined an oscillation as the 
warmest point. 
The differences between the annual ranges of temperature of the 
different directions of wind seem to point to the cause of this 
oscillation in the direction of the warmest wind, as being the degree 
to which the yearly march of temperature affects the areas over 
which these winds blow. The south-east wind has an annual range, 
