524 
Proceedings of the Royal Society 
on every side from which observations have been obtained, and that 
surface winds flow out of spaces of high pressure in every direction. 
This outflow of the winds from regions of high pressure, and inflow 
upon regions of low pressure, may be explained by the principle of 
gravitation. Indeed, so strongly is this force marked, on compar- 
ing isobaric lines with prevailing winds, that if there be any other 
force or forces concerned in setting the winds in motion, they 
must hold a very subordinate place. The influence of a mountain 
range in diverting aerial currents from their normal courses was 
illustrated by the prevailing winds in Norway; and an explanation 
was offered of the anomalous direction of the winds on the coast of 
West Greenland. 
The relation of the data, graphically delineated on the charts, 
to climate was pointed out ; for since winds bring with them the 
temperature of the parts of the earth’s surface they have traversed, 
the charts may be regarded as furnishing the key to the climates 
of different countries. Their relation to the rainfall of the different 
months of the year was adverted to. Thus, by a careful study of 
the isobaric lines, and the prevailing winds, in connection with the 
isothermal lines, the climate of any region may be more closely 
approximated to than has hitherto been possible. 
It was pointed out that the position of the isobaric lines in the 
different months appears to be entirely determined by the sun and 
the geographical distribution of land and water ; and since these 
lines, in their turn, determine the climates of the globe, there is 
here evidently a principle applicable not only to the present state 
of the earth, but also to other distributions of land and water in 
past times ; in other words, there is here a principle of the utmost 
importance to the geologist in attempting to account for glacial 
and warm periods through which the climates of Great Britain and 
other countries are known to have passed. If this conclusion be 
just, we are now in a position to give an approximate numerical 
statement of Lyall’s idea of the effect produced on climate by the 
displacements of continents. 
