He has also, as the result of observations, reduced the probable density of the atmosphere of Mars to 2-1/2 inches of mercury, or only one-twelfth of that of the Earth.
_Critical Remarks on Mr.Lowell's Paper._ The last part of this paper, indicated under pars.

4 and 5, is the most elaborate, occupying eight pages, and it contains much that seems uncertain, if not erroneous.

In particular, it seems very unlikely that under a clear sky over the whole earth we should only receive at the sea-level 0.23 of the solar rays which the earth intercepts (p.

167).
These data largely depend on observations made in California and other parts of the southern United States, where the lower atmosphere is exceptionally dust-laden.

Till we have similar observations made in the tropical forest-regions, which cover so large an area, and where the atmosphere is purified by frequent rains, and also on the prairies and the great oceans, we cannot trust these very local observations for general conclusions affecting the whole earth.