OF THE VELOCITY OF MOTION OF THE WAVE-PARTICLE. 79 



Placing the velocities obtained together they are — 



1. Cap of gate pillar 



2. Cap of Mr. Stewart's tomb 



3. Cemetery wall 

 Mean 



Mean, omitting No. 2 ... 

 Mean of means ... 



2116 



1622 



2185 



19-74 



21-5 



20-62 



"We may therefore say that the velocity of wave-particle at the sur- 

 face was not far from 20 feet per second. 



But, as I have before explained, there is good reason for supposing 

 that, in transmission from the lower to the superficial beds of clay, the 

 velocity of wave-particle was diminished, while the angle of emergence 

 was increased. From this it follows that the true velocity of wave- 

 particle was greater than 20 feet per second. Assuming that in trans- 

 mission no part of the vertical velocity was lost, then the vertical com- 

 ponent of the velocity of wave-particle, in what we may call the true 

 shock, was the same as that of the surface shock, which for a superficial 

 angle of emergence of 30° is one-half of the total velocity of wave- 

 particle at the surface, or say 10*5 feet per second. Taking the true 

 angle of emergence as 20,° we get the true velocity of wave-particle by 

 the formula — 



V = 10-5 x cosec. 20.° 

 = 30*7 ft. per second. 



This constitutes the evidence we have of the velocity of wave- 

 particle in the case of this great earthquake. Though sadly deficient, it 

 is at any rate definite ; it only gives the velocity at one station, but at 

 that station there is no lack of certainty. We have proofs of a velocity 

 of wave-particle of at least 20 feet per second, and by what I believe 

 to be a warrantable deduction we obtain a velocity as high as 30 feet 

 per second. Thus giving a velocity of wave-particle double that observed 

 by Mr. Mallet in the Neapolitan Earthquake of 1857, and that at a 

 distance of 85 miles from the seismic vertical against a distance of 



( 79 ) 



