202 



EAETHQUAKES. 



be taken, and three given points of observation, Aqj Aj, Ag, 

 be plotted on a piece of paper, it will be found that it is 

 not a difficult matter to determine two numbers propor- 

 tional to a and b which will allow you to draw two circles 

 so that they may be touched by a third circle drawn through 

 Aq. This pro lem has practically been applied in the case 

 of the arrival of a sea wave at a number of places on 

 the South American coast, at the time of the earthquake 

 of May 9, 1877. This is illustrated as follows. The 

 places which were chosen were Huanillos, Tocopilla, 

 Cobija, Iquique, Mejillones. 



In the following table the first column gives the times 

 at which the sea wave arrived at each of these places in 

 Iquique time; in the second column the difference 

 between these times and the time at which it reached 

 Huanillos is given ; in the third column the distances 

 through which a sea wave, propagated at the rate of 350 

 feet per second, could travel during the intervals noted in 

 the second column is given. 





Arrival of sea 



Time after 

 arrival at 



Distance at ! 

 850 feet per 







Huanillos 



second 





h. m. 



minutes 



mres 



Huanillos .... 



8 .30 











Tocopilla .... 



8 32 



2 



8 



Cobija 



8 38 



8 



32 



Iquique .... 



8 40 



10 



40 



Mejillones .... 



8 46 



16 



64 



The distances marked in the third column are used as 

 radii of the circles drawn round the places to which 

 they respectively refer. 



The centre of the circle drawn to touch the circles of 

 the first column, and at the same time to pass through 

 Huanillos, is marked c. 



