290 BOTANY, ETC., OF THE 
the elements most friendly to the intellectual development and progress 
of our race. 
Another and equally erroneous opinion prevails, that the mean 
summer temperature in America is as much higher as that of winter is 
lower in places situated under corresponding latitudes to others in 
Europe. That such is not the case, might easily be shown from 
registers from both continents ; but the subjoined examples, taken from 
Mahlmann's tables, giving the result of observations made at two 
places in Europe and America, under parallels almost precisely the same, 
and continued for nearly equal periods, may suffice to prove the truth 
of our assertions. 
ifieri eiia 
- 5 og g EE 32 
: =E E Z4 | oH 
= EI. - E = p^ 
Washington ...... 38 53 2 54°86 71:06* 36:14 78:08 | 30°42 
ER 6 5t 38 42 9 11 61:52 71:06* 52°44 72:14 52°16 
The higher temperature of Washington during a part of the summer 
months is doubtless due to its much more inland position, the absence of 
any great body of water, and the general aridity and want of shade 
which makes that city a singularly unpleasant residence in the hot 
season. Lisbon, on the contrary, has an almost insular position at the 
mouth of the Tagus, and is fanned by the breezes from that river and the 
adjacent Atlantic, above which its elevation is also something con- 
siderable ; yet we see that the heat of the entire summer coincides to a 
fraction at both places. So the summer-heat at Madrid fully equals 
that of Philadelphia, though half a degree north of the latter city. and 
at least 1,500 feet above the level of the sea. We may here remark 
by the way, that even in the low latitude of Washington the winter 
temperature is still several degrees below that of London and Paris, 
whose isocheimal curves will be found to have their concave summits 
in southern Virginia or on the confines of North Carolina, since it is 
not till arriving at Richmond in the former State that we begin to find 
* Mean of summer probably too low for both places. I am far from relying 
implicitly on the temperatures quoted from Kümtz or Forry, which are necessarily 
derived from sources of very unequal accuracy, and are too often the result of a few 
years only of observation. ^ Error is, indeed, apparent upon the face of many of 
dum them; but they are the best we can command, and in the main are near enough to 
the truth for establishing the facts here stated. 
