64 Prof. C. G. Knott on Reflexion and Refraction of 



The present result thus lies fairly close to the values of 

 Weber and of Lees, the difference between it and each of 

 these (extrapolating to 20° C. from the numbers given above) 

 being about three per cent. 



In conclusion, we hope to be able shortly to apply our 

 method to two problems upon which it seems desirable that 

 more work should be done — the temperature-coefficient of 

 water and the properties of solutions. Each of these measure- 

 ments amounts to the comparison of the thermal conductivities 

 of two liquids in different physical conditions, and the ex- 

 perience now gained of the working of our apparatus points to 

 its being particularly well adapted to such comparisons. 



III. Reflexion and Refraction of Elastic Waves, with Seismo- 

 logical Applications. By Professor C. Gr. Knott, D.Sc, 

 F.R.S.E.* 



AT Lord Kelvin's suggestion I reproduce, with additions 

 and extensions, a paper I published eleven years ago 

 in the ' Transactions ' of the Seismological Society of Japan. 

 This Society ceased to exist some years ago ; a fact which 

 may serve as a further reason for reproducing a paper, 

 in which the problem of the behaviour of an elastic wave 

 incident on the interface of rock and water was for the 

 first time fully worked out. In that paper also, I believe, 

 the sound method of treating the general problem when the 

 two media are elastic solids was first explicitly stated (see 

 below, pp. 71, 92). 



For convenience I have divided the present communication 

 into three parts. 



Part I. is a reproduction of my seismological paper of 

 1888 with a few verbal corrections. Footnotes added now 

 are enclosed in square brackets. 



Part II. contains detailed numerical calculations for rock- 

 rock interface and for rock-air interface, similar to the calcu- 

 lations for rock-water interface in Part I. 



Part III. gives the mathematical investigation and the 

 various sets of formulas on which these calculations are based. 



Part I.f 



Earthquakes and Earthquake Sounds : as Ulustrations of 

 the General Theory of Elastic Vibrations. 

 The first systematic application of the theory of vibrations 

 to the problems of earthquake motion was made, I believe, 



* Communicated by the Author. 



t [Read at Tokyo before the Seismological Society of Japan, February 

 23rd, 1888, and published in their ' Transactions ' of that year.] 



