238 DOVE ON THE NON-PERIODIC VARIATIONS IN THE 
winter of 1798-1799 was very severe in Europe, but mild in 
Umeo; while, in 1803-1804, there was a severe winter in Umeo, 
but mild weather in the rest of Europe. If we compare the de- 
scription of the Arctic regions of North America by British na- 
vigators, with Wrangel’s account of north Siberia, we perceive 
that here also important differences in the atmospheric relations 
arise from the configuration of the land. 
It appears therefore, from the above researches, that there is 
always an equal quantity of heat existing over the surface of the 
earth, but differently distributed at different times. Every ex- 
treme in one place is counterpoised by a contrary extreme in 
another; we have, therefore, no right to assume any other ex- 
ternal sources of heat than that of the sun. When the chain of 
observations shall be extended over a greater surface, more exact 
conclusions may be drawn, and the secondary phenomena di- 
stinguished from those that are primary. The tables may also 
be used to settle other questions: for instance, “ Whether there 
is any connexion between the appearance of comets, and the 
meteorological phenomena of the period? Whether volcanic 
eruptions or earthquakes are independent of atmosphericchanges? 
or whether they reciprocally produce each other? Observations 
at only one place are not sufficient to solve these questions ; we 
must know whether the relations on the earth were at the time 
of a comet, or of a widely extended earthquake, normal or ab- 
normal; whether the variations followed or preceded the phe- 
nomena. A certain connexion between volcanic occurrences, 
and great extremes of temperature, seems indeed to exist. 
(End of the First Part.) 
The volume, of which the preceding is an abstract, was pub- 
lished in May 1840; in 1841 Professor Dove published a second 
part, containing many additional tables, particularly those con- 
taining observations from North America, by which more light 
is thrown upon the opposite meteorological relations which fre- 
quently prevail in Europe and America. It has been shown 
above that the variation from the mean distribution of tempera- 
ture, as deduced from the observations of many years, is not a 
local phenomenon, but extends over a large surface, and there- 
