ON ITS EXTERIOR. ERUPTIONS OF GAS. 205 



danger and destruction are around him and beneath Ills 

 feet. Though such emotions are deeply seated, they are not 

 of long duration. The inhabitants of countries where long 

 series of weak shocks succeed each other, lose almost every 

 trace of fear. On the coasts of Peru, where rain scarcely 

 ever falls, and where hail, lightning, and thunder, are un- 

 known, these atmospheric explosions are replaced by the 

 subterranean thunder which accompanies the trembling of 

 the earth. Erom long habit, and a prevalent opinion that 

 dangerous shocks are only to be apprehended two or three 

 times in a century, slight oscillations of the ground scarcely 

 excite so much attention in Lima as a hail storm does in 

 the temperate zone. 



Having thus taken a general view of the active internal ter- 

 restrial forces ; of the earth's heat, its electro-magnetic cur- 

 rents, its auroral light, and the irregular action of those forces 

 at the surface of the earth, we will now proceed to the pro- 

 duction of material substances, and to the chemical changes of 

 which the crust of the earth and the constitution of the atmos- 

 phere is the theatre. We see steam and carbonic acid gas 

 issue from the ground almost always free from any admixture 

 of nitrogen ( 124 ), carburetted hydrogen gas (which has been 

 used for more than a thousand years in the Chinese province 

 of Sse-tchuan,( 195 ) and recently in the village of Eredonia 

 in the North American State of New York, both for culinary 

 purposes and for illumination), sulphuretted hydrogen and 

 sulphurous vapours, and more rarely sulphurous acids and 

 hydrochloric acid gas.( 196 ) The fissures of the earth from 

 whence the vapours and gases issue are not peculiar to 

 districts of active or of long extinct volcanoes, but occur 



