416 Scientific Intelligence. 
would se.em more applicable than many terms used in the de- 
scription of other seas.-— Gore Guseley’s Travels , vol. i. p. 152. 
45. Schmidt on the Height of the Atmosphere. — Schmidt, in 
his “ Ideen fiber die ursach der begranzung unsers Luft Kreisses 
et uber die besti miming der hbhe derselben in Gilbert’s Annar. 
len 1819,” conceives that the limit of our atmosphere is at that 
boundary, where the specific elasticity of the air is balanced by 
the power of gravitation. Calculation gives as the result, that, 
in those places where the mean temperature of the earth’s sur- 
face is 22° 4' R., the height of our atmosphere is equal to 7.22 
German miles. On the contrary, where it is 0°, the height is 
6^6 German miles. Beyond these limits, according to this con- 
ception, no air will occur. 
46. Account of a Cavern * of Lava . — The following interest- 
ing account of this cavern is taken from Dr Webster’s descrip- 
tion of St Michael’s : 
u Having reached a field between three and four miles NW. 
from the city, we discovered the entrance to the cavern. It is 
a fissure in the rocks, which here rise only a few feet from the 
surface, and is about wide enough to admit two persons abreast. 
The bottom, when viewed from the entrance, for some yards 
formed a gently inclined plane ; but as we proceeded, the rocks 
spread out on both sides, and we soon found ourselves in a spa- 
cious apartment, the floor of which was heaped with huge frag- 
ments of lava, that had fallen from above, and over which our 
progress was for some distance difficult, and rather dangerous. 
At the distance of ten or twelve yards from the entrance, we 
came suddenly upon the edge of a precipice, beyond which it 
seemed impossible to proceed. Creeping, however, with caution 
along the edge, we presently came to a point where an accumu- 
lation of fragments afforded a natural but dangerous passage, 
and, by leaping from rock to rock, we at last reached the bottom. 
“ The height of the precipice was probably not less than 
thirty feet ; and as the torches with which we were provided ser- 
ved to illuminate the cavern but feebly, we directed our guide to 
kindle a fire. From the sound of our voices, we were of opi- 
* The application of the expressive term cavernotis to the lava, has been adopt- 
ed, as Professor Silliman observes, from Sir George Mackenzie’s work on Iceland. 
