1888 - 89 .] Dr A. Buchan on Atmospheric Circulation. 791 
diurnal curve of lightning over the open sea is closely coincident 
with the evening maximum of pressure. The phases of the diurnal 
curves of the electric phenomena are these : — Thunderstorms over 
land, 2 to 6 p.m.; lightning over land, 8 p.m. to midnight; lightning 
over the open sea, 8 p.m. to 4 a.m.; and thunderstorms over the 
open sea, 10 p.m. to 8 a.m. 
Monthly , Annual , and Recurring Phenomena . — The following 
among other tables have been published with the Report : — Table 
IV., showing the Mean Diurnal Variation of Atmospheric Pressure 
at 147 Stations ; Table VI., the Mean Monthly Height of the Baro- 
meter at 1365 Stations; Tables VII. and VIII., the Mean Monthly 
Direction of the Prevailing Winds at 746 Stations; and Table IX., 
the Mean Monthly Temperature at 1620 Stations. The results of 
these data are represented on fifty-two large maps, giving for the 
months and the year the distribution over the globe of the 
temperature and pressure of the atmosphere, and the prevailing 
winds. These results were stated in some detail, from which the 
following broad conclusions were drawn : — This investigation shows 
in the clearest and most conclusive manner, that the distribution 
of the pressure of the earth’s atmosphere is determined by the 
geographical distribution of land and water in their relations to 
the varying heat received from the sun through the months of the 
year ; and since the relative pressure determines the direction 
and force of the prevailing winds, and these in their turn the 
temperature, moisture, rainfall, and in a very great degree the 
surface currents of the ocean, it is plain there is here a principle 
applicable not only to the present state of the earth, hut also to 
different distributions of land and water in past times. In truth, it 
is only by the aid of this principle that any rational attempt, based 
on causes having a purely terrestrial origin, can be made in explana- 
tion of those glacial and warm geological epochs through which 
the climates of Great Britain and other countries have passed. 
Hence the geologist must familiarise himself with the nature of 
those climatic changes, which necessarily result from different 
distributions of land and water, especially those changes which 
influence most powerfully the life of the globe. 
