208 



EAETHQUAKES. 



used as illustration for the two previous methods, we 

 obtain for the co-ordinates of Mejillones, Iquique, Cobija, 

 Toeapilla, and Huanillos, measured in geographical miles, 

 and the times in Iquique time at which the wave reached 

 each, as given in the following table ; ox and oy being, 

 drawn through Mejillones. 





Co-ordinates 



Time of arrival 





OX 



OT 



h. m. 



Mejillones 



« or 



J or 



8 46 p. m. 



Iquique . 



a^ 01- 150 



&i or 96 



8 40 „ 



Cobija . 



«2 or a 6 



h., or 14 



8 38 „ 



Tocopilla 



«3 or Q>Q 



&3 or 31 



8 32 „ 



Huanillos 



«4 or 102 



h^ or 58 



8 30 „ 



From this data we find the co-ordinates x and y of 

 this origin to be 85*8 and 56*7 ; whilst the velocity of 

 propagation = 45 feet per second. 



Measuring these ordinates upon the map, we obtain a 

 centre lying very near Long. 71° 5' W. and Lat. 21° 22' 

 S., a position which is very near to that which has already 

 been obtained by other methods. 



If instead of Huanillos we substitute the ordinates 

 and time of arrival of the sea wave for Pabalon de Pica, 

 another point for the origin will be obtained lying farther 

 out at sea. To obtain the best result, the method to be 

 taken will evidently be, first to reject those places at 

 which it seems likely that some mistake has been made 

 with the time observations, and then with the remaining 

 places to form as many equations as possible, and from 

 these to obtain a mean value. This is a long and tedious 

 process, and as the time observations of this particular 

 earthquake are probably one and all more or less inaccu- 

 rate, it is hardly worth while to follow the investigation 

 farther. 



In this example, as in the preceding ones, it will be 



