86 EAKTHQUAKES. 



no sensible effects are produced, whilst the same disturb- 

 ance may be recorded at a long distance from its origin 

 on the sm^face of the ground outside the tunnel. 



Lastly, we may refer to the experieuces of miners 

 underground. 



Occasionally it has happened that miners when deep 

 underground, as in the Marienberg in the Saxon Erzge- 

 birge, have felt shocks which have not been noticed on the 

 surface. These observations are rare, and it is possible 

 that they may be explained by the caving in of subter- 

 ranean excavations. 



The usual experience is, that if a shock is felt 

 underground it is also felt on the surface, as for example 

 in the lead mines in Derbyshire at the time of the 

 Lisbon disturbance (1755). 



The most frequent observation, however, is that a 

 shock may be felt on the surface while it is not remarked 

 by the miners beneath the surface, as at Fahlun and 

 Presburg in November, 1823. 



At the Com stock Lode in Colorado about twelve 

 years ago many earthquakes were felt. On one par- 

 ticular day twenty-four were counted. Superintendent 

 Charles Foreman told the author when he visited 

 Virginia City in 1882, that special observations were 

 made to determine whether these shocks were felt 

 as severely deep down in the mines as on the surface, 

 where they were on the verge of being destructive. 

 The universal testimony of many observers was that in 

 most cases they were not felt at all underground, and 

 when a shock was felt it was extremely feeble. At 

 Takashima Colliery, in Japan, it is seldom that shocks 

 are felt underground. 



The explanation of these latter observations appears 

 to be either that, in consequence of a smaller amplitude 



