242 DOVE ON THE NON-PERIODIC VARIATIONS IN THE 
be nearly equal at Rome and at Manheim; the polar cold is, on 
the other hand, much less at the former than at the latter sta- 
tion. The end of July, middle of September, and beginning of 
October 1789, offer good examples of the mountain cold, as do 
also February, March, and June 1791, and September 1792. In 
the middle of January of the last-named year, an increased tem- 
perature, spreading itself northwards from Rome, gradually re- 
pelled the cold which had previously prevailed to beyond Peters- 
burg; in February the cold polar current gained the mastery, 
and advanced towards the south. In the beginning of 1786 the 
maximum of polar cold was in Petersburg; by the end of Fe- 
bruary the cold had spread over the whole field of observation, 
being inconsiderable only in Rome, as was the case in November 
of the same year. In December 1788, both causes probably 
acted together. 
We see that the cooling influence of even such mountains as 
the Alps is inferior to that of extensive currents of air, and that 
they do not form such a complete separating barrier to the wea- 
ther as might have been imagined @ priori; the influence of the 
inequalities of the terrestrial surface, on the general meteorolo- 
gical relation, can therefore only be considered as subordinate in 
character. 
Quantitative equality, in the abnormal deviations at neigh- 
bouring places during the same epoch, points to the undisturbed 
action of general causes ; considerable differences in the amount 
of such deviations indicate local influences, which modify the 
action of these general causes differently at different places. A 
consideration of the Tables I. and II. appears to show that such 
local influences are less in England and Germany than in Ame- 
rica, which is probably owing to the more partial distribution 
of cultivation in the latter; however, in both continents local 
influences are very inferior to general ones. 
Table III. contains some striking confirmations of the con- 
clusions already drawn in the first part as to the occurrence of 
different extremes adjoining each other in an east and west di- 
rection. The severe cold of January 1838, and November 1829, 
in Europe, was fully compensated by the simultaneous high 
temperatures in North America, whither the cold did not make 
its way until February. In January 1837 the reverse took 
place, the weather being cold in America, and mild in Europe. 
