It is thus evident that Michell con- 

 ceived the vapour to continue to force 

 its way onward between the strata as far, 

 at least, as the earthquake continued to 

 be felt at the surface. His familiarity 

 with the regular and gently inclined 

 stratification of the rocks in the southern 

 part of England, and his experience that 

 at the surface of the ground they may 

 for the most part be easily split open 

 along their bedding-planes led him to 

 this belief. He imagined that the vapour 

 might be propelled even to the extreme 

 limits of the area affected by an earth- 

 quake, for he remarks in one place that 

 " the shortest way that the vapour could 

 pass from Lisbon to Loch Ness was under 

 the Ocean" (Art. 98 note). 



The same ingenious paper showed how 

 the centre or focus from which an earth- 

 quake is propagated may be ascertained 

 first, from observation of the different 

 directions from which the shock arrives 

 at several distant places : " if lines be 

 32 



