130 EARTHQUAKES. 



certainly, if applied in houses of the type described, would 

 be valuable. 



The great danger of fire may partially be obviated by 

 the use of ' earthquake lamps,' which are so constructed 

 that before they overturn they are extinguished. It is 

 said that in South America some of the inhabitants are 

 ready at any moment to seek refuge in the streets, and 

 they have coats prepared, stocked with provisions and 

 other necessaries, which, if occasion demands, will enable 

 them to spend the night in the open air. These coats, 

 called ' earthquake coats,' might also, with properly con- 

 structed houses, be rendered unnecessary. 



Destruction due to the natui^e of the underlying 

 rocks. — That the nature of the ground on which a 

 building stands is intimately related with the severity of 

 the blow it receives is a fact which has often been de- 

 monstrated. 



One cause of destruction is due to placing a building 

 on foundations which are capable of receiving the full 

 effects of a shock, and transmitting it to the buildings 

 standing on them. 



For instance, the reason why a soft bed might possibly 

 make a good foundation, is, as has been pointed out by 

 Messrs. Perry and Ayrton, because the time of trans- 

 mission of momentum is increased ; in fact, the soft bed 

 is very like a piece of wood interposed between a nail and 

 the blows of a hammer — it lengthens the duration of 

 impact. For this reason we are told that a quaking bog 

 will make a good foundation. When a shock enters loose 

 materials its waves will be more crowded, and it is possible 

 that a line of buildings may rest on more than one wave 

 during a shock. There are many examples on record of 

 the stability of buildings which rested on beds of particu- 

 lar material at the time of destructive earthquakes. As 



