TRANSACTIONS OF THE SECTIONS. 27 
North America from 30° to 51° N. lat. 
ADIT seeretaae eet s.70 SOR SN GOF e's. 
Europe ......... See SO? cog deny 
The British Isles are situated almost in the centre of this zone. To show the main 
features of their temperature, the author had constructed on a large map iso- 
thermals of the hottest and coldest month (July and January) in the year, based on 
the observations of about seventy places. 
The most striking feature in the January isothermals is their general direction 
from north to south, instead of from west to east, inferring the greatest cold not in 
the north, but in the east. Between the Shetland Isles and the southern coast of 
England (except Cornwall and Devon) there is no difference in the winter tempera- 
ture; but between the eastern coasts of England and the western coasts of Ireland 
the difference amounts to about 10°; the former being, at an average, 35°, the latter 
robably 45°. The coldest portion of Britain extends from the Naze to the Firth of 
orth, comprising to the west all the Pennine chain; in this district an average 
temperature of 35° to 36° prevails. On the continent the January temperature be- 
comes lower in going eastward, precisely in the same ratio as in the British Isles, 
and the isothermal of 28° extends as far west as the meridian of Gottingen and 
Hanover. In Scandinavia the temperature decreases very suddenly, owing to the 
snow-clad mountain masses which project in a high rampart on the western coasts. 
The difference between Bergen and Christiania, two places in about the same lati- 
tude, distant from each other 190 miles, amounts to as much as 14°, the former 
being 35°-0, the latter 20°°8. The author then proceeded to allude to general and 
local causes, by which these January isothermals are regulated. 
The average direction of the isothermals of the hottest month (July) is from S.W. 
to N.E. The highest summer temperature in the British Isles, indicated by the 
isothermal of 64°, occurs in the central portion of the south coast of England, the 
lowest in the N.W. part of Scotland, and the difference appears to be at least 10°; 
while the difference between the western and eastern coasts is much less. The iso- 
thermal of 62° extends to Lincoln, Birmingham, and the southernmost portions of 
Wales. All Ireland, Wales, northern part of England, and Scotland to the foot of 
the Highlands, lie between the isothermals of 62° and 60°. North of the Highlands 
the temperature is very considerably lower, Inverness having only 55°°7. By com- 
paring the British Isles with parts of the continent in the same latitude, we find in 
that of Dublin, 61°°5, at the Dutch shores 64°, at Hamburg 65°. In the latitude 
of Inverness (55°-7 temp.), Frederikshaven in Denmark 61°-9, G6oteburg in Sweden 
_ 63°°2; between this latter place and Inverness the distance is 600 English miles. 
The author then alluded to the influence of temperature on the distribution of 
plants, the districts of which he had found to be strikingly corroborative with the 
general correctness of his isothermals (for his botanical observations he was greatly, 
indebted to Mr. H. C. Watson, author of the ‘ Cybele Britannica,’ &c.). There are 
_ altogether a good number of plants in Britain which botanists are accustomed to re- 
gard as western species, being frequently scattered along the western counties, from 
Cornwall to Scotland, without passing into the eastern counties, unless at the south 
or north extremities of Britain. Compared with each other, these western species 
present much difference in respect to the area, or space of Britain, over which they 
are distributed respectively. But they correspond in the negative peculiarity of being 
absent from that part of Britain which extends between the Firth of Forth and the 
Lincolnshire Wash, and mostly absent from the whole eastern side of the island be- 
‘tween the Thames and Murray Firth. This class of plants corresponds in their di- 
stricts with the January isothermals. Other plants, less impatient of a cold winter, 
but requiring a higher summer temperature, are found to run parallel with the July 
isothermals. A great number of species, and the districts where they occur, were 
named. Among the more important plants being limited by summer isothermals is 
the vine, the northern limit of which is found to be between the July isothermals of 
66° and 67°. In the valley of the Seine, it obtains its highest latitude between Louvier 
and Andelys in about 49° north lat., but further east, near Berlin, it reaches nearly 
523°, a latitude corresponding with that of Norwich, Birmingham and Limerick. 
__ The author, in concluding his observations, expressed the hope to see this subject 
farther investigated ; especially to see the net of meteorological stations over the 


































