were often thrown. "If," he asked, 

 "when the vapours find a vent, they are 

 capable of shaking the country to the 

 distance of ten or twenty miles round, 

 what may we not expect from them when 

 they are confined? ' 



He stated that " the motion of the 

 earth in earthquakes is partly tremulous, 

 and partly propagated by waves which 

 succeed one another, sometimes at larger, 

 sometimes at smaller distances, and this 

 latter motion is generally propagated 

 much further than the former 1 ." He 

 believed that both of these motions could 

 be accounted for by the steam generated 

 as assumed. " Let us suppose," he re- 

 marked, " the roof over some subter- 

 raneous fire to fall in. The earth, 

 stones, etc., of which it was composed 

 would immediately sink in the melted 

 matter of the fire below : hence all the 



1 Art. 1 1 of the paper. Michell appears to have 

 been the first to point out that the earthquake travels 

 in successive waves through the earth. 



28 



