of Edinburgh, Session 1872-73. 
79 
2. The Meteorology of the Month of May. By Alexander 
Buchan, M.A. 
Excepting the months of January and July — the months of 
extreme temperatures for the larger portions of the globe — there 
is no month the meteorology of which is so peculiar, and a careful 
investigation of which is so likely to lead to striking and important 
results, as the month of May. The peculiarity of the meteorology 
of the month of May is, that it is the month of the year during 
which the most rapid rise of temperature takes place over the 
greater parter part of the northern hemisphere, and the most rapid 
fall over the greater part of the southern hemisphere ; and since 
that rapid rise and equally rapid fall takes place at very different 
rates, according to the peculiar distribution of land and water in 
each region, the inquiry is calculated to bring out in strong relief 
some of the more prominent causes which influence climate, and 
some of the more striking results of those causes. The method of 
inquiry which has been adopted was to compare the average atmo- 
spheric pressure of May with that for the year, setting the differ- 
ence of excess or deficiency in their proper places on maps, and 
drawing therefrom lines of equal deviation from the annual mean, 
for every 0T00 inch, and in some cases for 0-050 inch. The winds 
had been dealt with in a similar way — viz., by finding the difference 
between the average of May and the general monthly averages of 
the year. From these two elements — distribution of pressure and 
winds — the rainfall and other elements of climate necessarily 
follow. The results of the inquiry which has been made, and 
which was based upon observations at upwards of 600 places, show 
a diminution of pressure in May over tropical and sub-tropical 
regions, and also over the north of Asia and to the south of South 
America and Tasmania. The excess of pressure in the northern 
hemisphere prevails over North America (to the north of the 
Lakes), over Arctic America, over Greenland, over the British 
Isles, and to the north of a line passing through the English 
Channel, in a north-easterly direction, to the Arctic Sea. Excess 
in the southern hemisphere includes the southern half of South 
America and of Africa, the whole of Australia, and the adjacent 
parts of the ocean. The influence of land in the southern hemi- 
VOL. VIII. 
