74 REPORT — 1900. 



tude as those which have been propagated over the beds of deep oceans. 

 Were the large waves of earthquakes mass waves, it is assumed that the 

 damping effect of oceanic waters would be insignificant. 



When considering the large waves to be distortional mass waves, an 

 observation of importance is that they travel from their origin to their 

 antipodes in about 110 minutes (see fig. 1). If the path was along a 

 diameter, the average velocity of propagation must therefore have been 

 1'9 km. per second, which is ^practically the so-called initial velocity. The 

 close correspondence of these two velocities suggests the idea that there 

 has not been any symmetrical change in the velocity of propagation of 

 waves through the earth with regard to its centre, or, in other words, the 

 large waves have had a diametral velocity which is practically constant. 

 This idea of a constant velocity for all depths indicates that arcual and 

 diametral velocities should be equal, which is not the case. An escape 

 from the dilemma is to suppose that the large waves do not pass through 

 the earth, but round its surface. 



12. Criticisms and Analyses by Dr. C. G. Knott. 



In reference to the conclusion implied in the last paragraph. Dr. Knott 

 remarks that it does not necessarily follow from the premises, the initial 

 speed referred to being an arcual speed, or a speed for short distances 

 from an origin through the surface layers. When a disturbance travels 

 straight down it very soon gets probably into more homogeneous materials 

 beneath the crust. It may therefore be a mere coincidence that the 

 average speed along a diameter may come out almost exactly the same as 

 the arcual speed in the crust. 



The evidence seems to show that once you get into the nucleus proper, 

 the speed of the large waves decreases with depth. But this does not 

 prevent the speed suffering a distinct increase when the disturbance passes 

 from the lower layei's of the crust into the higher layers of the nucleus. 

 That the arcual speed should be 1"9 for small arcs, and then become on 

 the average three when the arc is half a circumference, seems to be an 

 immeasurably more difficult thing to understand than that the speed 

 downwards should first increase and then decrease as the depth increases. 

 A not improbable change in the nature of the material could easily 

 account for the latter vai'iation ; but it is dithcult to see how a surface 

 ■wave of the size of the large waves could gain in speed as it ran round the 

 earth. 



Writing more generally respecting the propagation of large waves, 

 Dr. Knott says : — 



I have looked pretty carefully into your numbers and curves, and now 

 I shall indicate some of my conclusions. As you have pointed out, the 

 one doubtful point is the precise instant at which the disturbance began, 

 also to some extent the exact position of the origin. I take your deter- 

 minations as being as accurate as they can be obtained, and proceed to 

 consider the speeds indicated. The accompanying tables will show you 

 what I have tried to do. Take the Alaskan group, the most complete of 

 all you have. It is gratifying to find how similar the results are for the 

 three different earthquakes. The greatest discrepancy is in the two 

 numbers for the Batavian records. It is curious that these time records 

 do not fit well into the general scheme. Can there be any mistake 1 The 

 arcual speed indicated is distinctly smaller than we find in all the other 



