a Theory of the Earth * 830 
thunder, lightning, positive or negative electricity, sub» 
terranean noise, earthquakes : scoriae, ashes, and stones 
thrown up ; to what height and distance. 
5. Smell of the smoke. In general it indicates the sul- 
phureous acid; but it may indicate also bitumen and 
coal. 
6. Nature of the gases which escape during the erup- 
tion. 
7. Velocity of the lava. Its degree of fluidity com- 
pared with the inclination of the ground over which it 
flows. 
8. To measure, if possible, the degree of its heat 
when it issues from the volcano. 
9. Whether the lava appears to be in a state of com- 
bustion, or only incandescence. 
10. Whether it does not cool more slowly, and accord- 
ing to other laws, than that of the bodies heated or melt- 
ed in our furnaces. 
10. A. Can it be supposed that the matter thrown up 
by volcanoes was not inflamed, or even in a state of in- 
candescence, in the bowels of the earth ; and that it is 
only the contact of the air which gives it these qualities? 
11. Whether the sudden cooling of lava in the air or 
in water divides it into prismatic columns, such as those 
of basal tes. 
13. Whether it be true that scoria newly thrown up, 
and suddenly cooled by its rapid passage through the 
air, seems covered with a bituminous varnish. 
13. And, in general, whether the mountain throws up 
bituminous matter or any thing that resembles the resi- 
duum of the combustion of coal, or whether it rather 
throws up pyrites or the residuum of their decomposition* 
14. To ascertain by observations, and even by expe- 
riments, whether it may not be possible that pyrites or 
other ferruginous matters decomposed by water, undergo 
Vol. i. t t 
