7 
22 On the Changes of Temperature and Sait 
fogs which. prevail therey haye never been. explored, and 
therefore remain unknown. This immenfe country cer- 
tainly extends nearer the north pole than the Continent of . 
Europe and Afia, the boundaries of which ate pretty well 
known. This, without doubt, may be reckoned among the 
‘oaufes which render North America much colder than’ Eu- 
rope under the fame degrees of latitude, as I have already 
remarked. Hence it happens that the immenfe Continent 
of America, the farther it extends towards the north, is more 
filled with lakes and marfhes, which muft confequently add 
to the feverity of thetwinds that fiveep their furface. , 
It will perhaps be faid, that it appears to follow, from my 
pofitions, that the more the cold of winter decreafes, from 
the above cqufes, the heat of fummer ought to increafe in 
the fame proportion. In my opinion it can be proved by 
many monuments, hiftorical as well as phyfical, that the 
fum-total of the mean fummer heat is greater than it was 
formerly, and that it continually incre: Foss though this takes 
place imperceptibly, and cam be obferved only aie periods 
ef confiderable Jength, and by comparing the reipective de- 
grees of dutant epochs. On the other hand, in regard to 
the degree of the intenfity of that penetrating, concentrated, 
and {iifling heat which is experienced even in Lapland, I 
mut fay, that this kind of héat-i is lefened by all thofe caufes 
before enumerated which leffen the cald of winter. -I by na 
means afcribe contrary effets to the fame caufe. Weare 
taught by general experience, that the thinner, purer, and 
more ela(tic the air is, the lefs, in the fame proportion, is 
the intenfity of the fummer heat; and, on the contrary, the 
thicker the atmofphere is, and the more it is filled with {tag 
nant and concentrated vapours, the heat is more intenfe and 
the more ftifling. For this reafon it is always cooler on the 
fummits of high mountains, while a fiifling and infupport- 
able heat prevails ; in the neighbouring plains, efpecially when 
they are furrounded by Tat This is always obferved in 
the favannahs of America. Dr. Williamfon was convinced, 
by experiments and obfervation, of the truth of my affertions 
in regard to North America; and he remarks, that when 
this extenfive coumtry becomes entirely open, when, sits 
g woods 
oo 
: 
: 
