1815.) Reyal Institute. ° 147 
Nature continued from the month of September, 1759, till next 
‘February. Eye-witnesses declare that the noise was equal to what 
would have been produced by thousands of cannon, and that it was 
accompanied by a burning heat, part of which still: continues 3 for 
M. de Humboldt found the heat of the soil 36° Fahr. higher than 
that of the atmosphere. Every morning thousands of columns of 
smoke rise from the cones and the crevices of that great platform. 
The two rivers now contain hot water impregnated with sulphureted 
hydrogen ; and vegetation is only beginning to appear upon this 
shattered country. 
This volcano is 46 leagues from the sea, and nearly as far from 
the nearest active voleano. On this occasion M. de Humboldt 
remarks that several volcanoes of the New World are at as great a 
distance from the sea as this is; while in the Old World we know 
no volcano that is 12 leagues distant from the sea, and the greater’ 
number are upon the shore. This scientific traveller informs us, 
likewise, that all the great volcanoes of Mexico are found not 
merely in almost the same line transversal to the direction of the 
Cordileyras, but likewise within a few minutes of the same parallel, 
as if they were all elevated above a subterraneous crevice which 
extends from sea to sea. He ascertained all these facts by measures 
and determinations of positions, as exact as troublesome to take, 
The public will see the whole details in the continuation of the 
celebrated work in which M. de Humboldt has consigned the result 
of his great work on America. 
M. de Humboldt, in a memoir on vegetation in the Canary Isles, 
has stated some general considerations on the geography of plants, 
By combining th. results.of observation with the double influence 
which the latitude and the height in the atmosphere produces on the 
temperature, he has fixed for a certain number of points the limits’ 
of perpetuak snow, the mean temperature of the air at that limit 
taken during the whole year, and likewise the particular temperature 
of the winter and summer months; and he has shown that we may 
deduce from these different data the habitual distance between that 
limit and the heights on which trees and corn grow; and that even 
the. variations, apparently capricious, which the same species of 
trees present in different climates, may be explained when we join 
to these data the consideration of the period of the year when each 
tree increases in bulk. 
It has been Jong known that the number of stigmata is not con- 
stant in the family of cyperee; nor was it believed that these 
Variations were sufficiently important to serve as a basis for the dis- 
tinction of the yenera. 
_M. Schkuhr, a German botanist, first observed that in the genus 
carex there exist species with two and three stigmata, and 
that the number of these organs is always the same as that of the 
engles of the fruit. 
Our associate, M, the Baron de Jeauvois, has generalized this 
observation to all the plants of the family. He has remarked some 
gE’ 2 
