72 



HEPOKTS ON THE STATE OF SCIENCE. 



Nos. II., III., XL, and XII., the duration at the commencement and at 

 the end of the movement is practically the same. It cannot be said to 

 be less. For the remainder the duration at tlie eud is distinctly greater 

 tlian near the beginning. The greatest duration has generally been in 

 regions lying between 70° and 110° from an origin; that is to say, in 

 a quadrantal region where amplitude is least and approaches a constant 

 value. 



/ The following is a list of the twelve earthquakes employed, with their 

 origins and the number of observations which were used in determining 

 each curve : — 



For Nos. 1-6 only records from Milne instruments were employed. 

 For the remainder the records were obtained from stations for the most 

 part employing Milne instruments, but not in all cases. One explanation 



Fig. 4. 

 Duration of Selected Eartliquahcs in relation to Distan e. 



250\ 



Degrees. t- t- >. -r- 



C5 o o 

 lO <« t^ 



oo 



for the observations which have been made upon amplitude and duration 

 is that at the time of a very large earthquake the material inside our 

 earth is moved as a whole, 



