BRITISH MEAN TEMPERATURES. 
47 
as giving only the main characteristics of the mean monthly 
temperature over our Islands. So soon as details are entered into 
it will be found that in contiguous districts considerable varia- 
tions are occasioned by purely local influences, such as the lie 
of the land, the drainage, the amount of wood in the neigh- 
bourhood, and the quality of the soil. For instance, in the 
Thames valley the general surface clay is pierced in several 
places by the sandy, gravelly stratum which underlies it ; and 
observations of the temperature of the air, made simultaneously 
over the different soils, would probably give very different 
results. After a shower of rain the water would soon disappear 
from the loose sandy soil, and the sun’s rays would immediately 
heat the earth and the superincumbent layer of air ; while on 
the clay the water would remain and keep the temperature 
down. Thus, while the isotherms on the different charts give 
the main distribution of temperature, due allowance must be 
made for such local influences as have been described above. 
The different cereals with which a farmer is principally con- 
cerned, though showing considerable climatic adaptability, are 
yet very sensibly affected by the temperature, and their profit- 
able cultivation can only be carried on within strictly defined 
limits. Thus, wheat cannot be grown with profit in the north 
of England at a greater elevation than 700 feet above the mean 
sea level ; and in the Orkneys, though it has been repeatedly 
tried, and generally produces an abundance of straw, the grain 
is seldom of any service. Oats, rye, and barley show a much 
wider geographical range than wheat ; but neither oats nor rye 
can be grown profitably in the Faro Islands, and though barley 
is still cultivated there the success is very limited. This is 
due to the strictly insular character of the climate of these 
Islands; for in Norway, in lat. 71°, or about 10° lat. further 
to the northward, both barley and rye grow freely, adapting 
themselves to the short, hot summer which prevails on the 
Continent in those latitudes. In fact, such is the speed with 
which vegetation progresses in situations from which during 
the summer the heat and light of the sun are scarcely ever 
withdrawn, that sixty days is the ordinary interval between 
sowing and reaping.* 
To the doctor a knowledge of the climate of the different 
parts of our Islands is of immense importance as determining the 
health resorts most suitable to the various patients under his 
care. It appears from statistics that the moist, equable climate 
which characterises the west coasts of Ireland and Scotland 
is much more healthy than that of England, and still more so 
than that of the continent of Europe ; so that the percentage 
Morton’s “ Cyclopaedia of Agriculture.’ 
