EARTHQUAKE MOTION DEDUCED FROM EXPERIMENT. 63 



these experiments tremors were observed as preceding and 

 following the main shock. 



Abbofs Results, — The important results obtained bj 

 General Abbot are contained in the following table : — 



§ 







S^ 



^^ 



a 



•^•-d 







0) "^ to 



o g 



>,?i'^ 



• > 



Date 



Cause of Shock 



g§3 



ai 



41. !^ 53 









.11 s 



b| 





§ 







pec 



^ 



> 



1 



Aug. 18, 1876 



200 lbs. of dynamite 



5 ± 



B 



5,280 



2 



Sept. 24, 1876 



Hallet's Point Explosion 



5-1.S4 



A 



3,873 



3 



»> 



»> »> » 



8-330 



B 



8,800 



4 



»> 



»> j> » 



98.33 



A 



4,521 



5 



„ 



?» >» V 



12-769 



B 



5,309 



6 



Oct. 10, 1876 



70 lbs. dynamite 



1-360 



A 



1,240 



7 



Sept. 6, 1877 



400 „ 



1-169 



A 



3,428 



8 



J, 



»i >» »» 



M69 



B 



8,814 



9 



Sept. 12, 1877 



200 „ 



1-340 



A 



6,730 



10 



>» 



" »» »» 



1-340 



B 



8,730 



11 





70 „ 



1-340 



A 



6,559 



12 



" 



)» »> »» 



1-340 



B 



8,415 



A seismometer of type A means that the telescope 

 used in observing the tremor produced on the surface of 

 a vessel of mercury by the 

 passage of the shock had a 

 magnification of 6, whilst a 

 telescope of the type B had 

 a magnification of 12. 



The mean velocity given 

 by six observations with type 

 A is 4,225 feet per second, 



while that given by the same number with type B is 7,475 

 feet per second. 



If we assume that the first tremor observed in the 

 mercury is to determine the true rate of transmission, 

 Greneral Abbot tells us that we must reject all observations 

 made with type A, inasmuch as they do not reveal the 

 velocity of the leading tremor. However, he also tells 



