May 15, 1884] 



NA TURE 



61 



the introduction of spherical balls of bell-metal working motion of the upper over the lower part of the building." 

 in cups of the same material placed between two platforms, j The cost of this was about 90/. for each lighthouse, 

 the lower cups being fixed to beams forming the foundation, This plan had some disadvantages : high winds, for in- 

 and the upper cups being fixed to the lower beams of the stance, gave as much free motion to the upper part as a 

 superstructure, thus admitting, within a limited range, free | slight earthquake would do : and there was also consider- 



© 



CENTRAL AREA 



Map of the Earthquake of April 22, 1884. N.B.— The places marked are those at which the shock was kit. In the East of England only the more 



important of such places are marked. 



SEA LEVEL, 

 1000 FT BELOW- 



-PAb 



W® 



KCW LONDON 



TtBS 



*0 



16 



'"OCks 



1 



1. Palaeozoic Rocks (Carboniferous and Older); 2, Permian to 



able movement of the lights during cleaning. The light- 

 house-keepers, therefore, screwed up the metal plates, so 

 that when an earthquake came sufficiently powerful to 

 test the value of the plan, the structure was rigid and the 

 glasses were broken. This plan was afterwards aban- 

 doned, and Mr. R. H. Brunton adopted the plan of con- 



structing the lighthouses with " great weight and solidity, 

 thereby adding to their inertia and checking the oscilla- 

 tion." Mr. W. Lloyd, from his experience in South 

 America, believes that the more solid the structures the 

 better they resist earthquake shocks. Mr. Woods, on the 

 other hand, found that in Peru lightly-built structures of 



