Dr. C. Davison — The Staford Earthquakes of 1916. 307 



Sound-Phenomena. 



Sound-Area. — The boundary of the sound-area is represented on 

 the map of the earthquake by the dotted line. This lies between the 

 isoseisraals 4 and 3, and includes an area 177 miles long, 157 miles 

 wide, and containing about 21,000 square miles. 



Within the whole area, the sound was heard by 77 per cent of the 

 observers. The decline in audibility, as the sound-waves progressed 

 outwards, follows the same law as in other strong earthquakes, 

 being 98 per cent within the isoseismal 7, 96 per cent between the 

 isoseismals 7 and 6, 83 per cent between the isoseismals 6 and 5, 

 57 per cent between the isoseismals 5 and 4, and 31 per cent outside 

 the last isoseismal. For the Derby earthquake of 1904, which 

 closely resembles the Stafford earthquake, the corresponding 

 percentages are 94, 93, 79, 56, and 38. 



Nature of the Sound. — The sound is described by 663 observers, 

 In 53 per cent of their records the sound is compared to passing 

 traction-engines, motor-cars, etc., in 7 per cent to thunder, in 9 to 

 wind, in 8 to loads of stones falling, in 9 to the fall of a heavy body, 

 in 12 to explosions, and in 2 per cent to miscellaneous sounds. 



The variation in the nature of the sound with the distance from 

 the epicentre is shown in the following table, in which the figures 

 are percentages of comparison to the different types for each of the 

 districts mentioned : — 



Omitting the references to miscellaneous sounds, the types of 

 passing vehicles, thunder and wind are of long, and the others of 

 short, duration. The percentages of reference to types 'of long 



