458 MK. R. D. OLDHAM ON THE CONSTITUTION [Aug. I906, 



regards the first phase, the conclusion was only one which had 

 already been suggested, and is still generally held ; but, as regards 

 the second, my interpretation has been traversed in two separate 

 ways. 



The first is by the Rev. 0. Fisher, who, believing my interpretation 

 to be inconsistent with his theory of the earth, has propounded a 

 most ingenious explanation of these second-phase waves. 1 It does 

 not seem to me that there is any insuperable incompatibility between 

 Mr. Fisher's theory of a fluid centre and the hypothesis that the 

 second-phase waves are distortional. We know nothing of the 

 behaviour of matter exposed to the pressures prevailing in the interior 

 of the earth, and it is not wholly inconceivable that a fluid under 

 pressure of millions of atmospheres might be enabled to transmit the 

 distortional waves which it is unable to transmit under pressures with 

 which we are familiar. I do not, however, insist on this point, as 

 it is immaterial to my present purpose : all that is material is that 

 the wave-motion, in the first and second phases, differs essentially ; 

 and this is accepted by Mr. Fisher. 



It is also indicated, apart from the arguments which I have already 

 urged, 2 by the records of Prof. Vicentini's type of seismograph, 

 composed of* two heavy masses, one free to move horizontally, the 

 other free to move vertically. In the records of great earthquakes 

 originating at a distance of 90° of arc or more, it is found that the 

 former gives a very small displacement for the first phase, while the 

 latter frequently registers the maximum displacement of the whole 

 disturbance. In the second phase the conditions are reversed, and, 

 while the mass free to move vertically seldom gives any indication of 

 disturbance, that which is free to move horizontally gives a very large 

 displacement. This difference in the character of the record in the 

 two phases shows that the movement is different, and incidentally 

 tends to support the interpretation that I have proposed : for, if the 

 first phase represents the outcrop of a disturbance transmitted 

 through the earth as a condensational wave, then vertical movement 

 would preponderate over horizontal at distances of 90° or more ; 

 while, if the second phase is caused by distortional waves, horizontal 

 movement should preponderate in it. 



This difference in the character of the records of the two phases 

 may also be used as an argument against the idea which has been 

 adopted in Japan, 3 that the first and second phases represent wave- 

 motion of similar character, transmitted at different rates through 

 layers at different depths from the surface, but in both cases parallel 

 to, and at no great depth below, it. As this contention is incompatible 

 with the figures given below, it need not be dealt with in this place, 

 and the facts may be left to speak for themselves. 



1 ' On the Transmission of Earthquake-Waves through the Earth ' Proe. 

 Cambridge Phil. Soc. vol. xii (1903-1904) pp. 354-61. 



2 Phil. Trans. Roy. Soc. ser. A, vol. cxciv (1900) pp. 162-66. 



3 A. Imamura, Publications of the Earthquake-Investigation Committee in 

 Foreign Languages, No. 16, Tokio, 1904 and later issues passim. 



