071 the Climate and Af/riculture of the British Isles. 49 
visitor in April and May. But the most powerful and persistent 
wind throughout the year is the warm and moist south-wester : 
it is most prevalent in July and August, at this season often 
bringing wet harvest weather ; it reaches a second and inferior 
maximum in December, driving back the Continental cold 
till after Christmas, and its inlluence is often felt through 
January. 
Our two prevailing winds, the south-west and north-east, arise 
from the same cause as true land and sea-breezes, — viz., the un- 
equal distribution of heat over the land and the sea. On the 
west of these islands, as I have shown, lies the wide Atlantic, 
with a surface heated to 54° in early spring. On the east, the 
continent of Europe has a temperature from 30^ to 40^ lower of 
cold, dry air, which becomes extreme in the north-east ; and the 
variable nature of our climate arises from the winds as they 
prevail from these quarters. Let the cold from the north-east be 
ever so intense in winter, the powerful westerly wind will drive 
it back, occupy its place, and day after day the thermometer 
will stand at 50'. 
The low lands of our eastern coast are exposed to the full 
power of the cold north-east wind of spring, which also sweeps 
unchecked over the central plain of England and settles down at 
night, with aggravated severity, in the valleys of the Trent and 
the Thames. If it blows long enough, it falls over the brow of 
the Cotswolds on the Vale of Berkeley, sweeps through the gorges 
of our western hills, and then mingles with the warm air of the 
Atlantic coasts, where the warmth from the sea materially alters 
its character. The great cold from the east wind on the 23rd 
of December, 1860, produced a minimum temperature in the 
valley of the Trent, near Nottingham, of 8° below zero ; in the 
valley of the Thames 3° below zero. At Truro the lowest 
reading of my thermometer was 13', and at Tresco Abbey, in 
the Scilly Isles, it was 24°. Thus in a period of extreme cold 
the warmth communicated from the sea maintained on our 
western coast a temperature of 32° above that of the eastern 
lands. 
The weather of January last affords us an instructive example 
of the influence of these winds on climate and their effects on 
agriculture. The new year dawned in a perfect calm ; but on the 
2nd, 3rd, and 4th, with a north-easterly wind, the whole country 
was covered with snow to an average depth (in Cornwall) of 6 
inches. The thermometer marked at Datchet 8°, Staines 7°, 
Wallingford 5°, all below zero ; at Penarth, Truro, 26°, and at 
Tresco Abbey, Scilly Isles, 33°, The wind gradually veered to 
the south-east, when a storm of unexampled fury burst on the 
VOL. IV. — g. S. E 
