ON THE MONTHLY ISOTHERMAL LINES OF THE GLOBE. 91 
and distribution of land and sea, they must have been different when these 
proportions and distribution were different. Generally speaking, the rising 
up of new masses of land must have condensed a certain quantity of the 
existing aqueous vapour, from the proportion of latent heat having been 
changed ; but the place where the solid mass was elevated must be of the 
greatest importance in this respect. ‘Thus considerable atmospheric convul- 
sions would have been amnong the secondary consequences of sudden geolo- 
gical revolutions, until the movements of the atmosphere had become accom- 
modated to the new circumstances of the surface on which it rests. Speaking 
generally, the temperature of the entire surface of the globe must have aug- 
mented with every augmentation of the solid portion of its area, 
If we now return to the consideration of the annual periodical variation of 
temperature over the whole surface of the globe, it may-appear surprising to 
find that it is greater than that of the southern hemisphere taken separately ; 
‘the variation of the whole globe being 33° Reaumur, or 8° Fahrenheit } and 
that of the southern hemisphere only 2°°6 Reaumur, or 5°°9 Fahrenheit; 
whilst the variation of the northern hemisphere is 9°°8 Reaumur, or 22°2 
Fahrenheit. It is only the two latter values however which can be properly 
compared with each other ; for the difference between the periodical variation 
of the northern and the southern hemispheres expresses the difference of effect 
produced by the variation of the sun’s meridian altitude in his annual course, 
according as land or sea predominate in the surface which receives his rays: 
the annual variation of the temperature of either hemisphere taken separately, 
being due to the variation in solar action, the receiving surface remaining 
the same. The annual variation of temperature of the whole earth, on the 
contrary, arises from the periodical variation in the surface brought under the 
sun’s rays, with no inequality in the conditions under which those rays are 
dispensed. 
We will now consider more closely the manner in which the position and 
form of the isothermals alter from January to July. 
The concavities of the January isothermals fall,—in America in the middle 
of the continent;—in the Old World, although still in the interior, yet much 
nearer to the eastern than to the western coast: the convex summits are in 
the intervening oceans. The isothermal curves rise steeply from Labrador 
to Spitzbergen, and descend almost perpendicularly to the European coast; 
from Norway to Nova Zembla, their eastern sides even form overhanging 
summits. The influence of the Gulf-stream is unmistakeable. The line of 
0° Reaumur, or 32° Fahrenheit, passes from Philadelphia across the banks 
of Newfoundland, and through the southernmost part of Iceland up to the 
Polar circle, which it reaches ‘in the meridian of Brussels. It thence descends 
quite perpendicularly, or in the direction of the meridian, to Holland, from 
whence it proceeds in a south-easterly direction to the Balkan: from the 
middle of the Black Sea it runs in a west and east course across Asia to the 
Corea, whence it rises to the Aleutian Islands and descends again in America 
to the latitude of Palermo. Thus we find that if we proceed in January from 
the Shetland Islands down the east coast of Great Britain to the channel, we 
do not alter the temperature, whilst with every step to the westward it 
becomes warmer, and that in no inconsiderable degree ; since both the west 
coast of Ireland and the extreme point of Cornwall are beyond the line of 
4° Reaumur, or 41° Fahrenheit. In Scandinavia the circumstances are still 
more extraordinary: from the intervention of the British Islands, the south- 
ern parts of Norway are less open to the warm sea current than the northern 
parts, and hence in the month of January the temperature actually becomes 
