meafuring Heights with the Barometer . 753 
of the North-eaft and South-weft wind^ on that inftru- 
ment, fuggefted with regard to the different denfities of 
the atmofphere in the different zones of the earth. 
But fince the experiments on the expanfion of moift 
air have fhewn its elafticity to be fo much greater than 
that which is dry, I apprehend, that the fimple principle 
of heat and moifture may fuffice to account for all the 
phenomena. Thus it is univerfally admitted, that there 
is a greater degree of humidity and heat in the air, near 
the earth’s furface, than there is in the higher regions of 
the atmofphere. The elafticity or expanfion of the 
lowermoft fecftion (q) of every column of air, whether 
long 
(p) I. have been well informed, that in China the North- weft wind raifes 
the barometer mold, and is highly electrical; it is at the fame time the drieft 
and the coldeft; and at Canton, under the Northern tropic, there is frequently 
ice. On the Eaft-coafts of North America the feverity of the North-weft 
wind is univerfally remarked ; and there can fcarcely be a doubt, that the inha- 
bitants of California, and other parts on the Weft-fide of that great Conti- 
nent, will, like thofe on the Weft of Europe, feel the ftrong effeCts of a North- 
eaft wind. The extraordinary drynefs and denfity of the wind from the ..North 
pole, feems therefore to be occafioned by its palling over the Continent ot 
Europe and Alia on one fide, and that of North America on the other. I hole 
who live on the Eaft and Weft-coafts of South America, will find the drieft 
and coldeft winds come to them refpeCtiveiy from the South-weft and South- 
ealt. As the winds feem to be colder, drier, and denfer, in proportion to the 
extent of land they pafs over from the poles towards the equator, fo they appear 
to be more moift, warm, and light, in proportion to the -extent of Ocean they 
pais over from the equator towards the poles. Hence the humidity, warmth. 
and lightnefs, of the Atlantic wind to the inhabitants of Europe. 
(q) Mr. de luc feems to have fnfpeded fomething of this k 
5 D 2 
kind towards the 
end 
