590 Transactions. — Chemistry and Physics. 



the indications given, with the same origin. There is no 

 other shock since the present system of records was be^fuu 

 (i.e., 1890) the data of which are sufficient to determine the 

 epicentrum exactly — in other words, the epicentra given in- 

 clude all those ascertainable at present. 



A circle of seven miles radius would include all the points 

 except A, and I think I may justly claim to have found, 

 within the limits of error of our present observations, the 

 region whence the great majority of the Cook Strait earth- 

 quakes proceed. 



The new instruments about to be set up in the colony 

 will, though not primarily intended for that purpose, no doubt 

 give us information that will help us to determine other ele- 

 ments, especially the period of the vibrations, and, if set up 

 in the proper plane, the amplitude of the vibrations. Hence 

 we can calculate the intensity of shock and the wave-length, 

 and may be led to reasonable speculation on the nature of 

 the underlying rocks between the origin and the place of 

 observation. 



Akt. LX. — Notes on the Comparison of some Elements of 

 Earthquake Motion as observed in New Zealand, loith 

 their Theoretic Values. 



By George Hogben, M.A., Secretary of the Seismological 

 Committee, Australasian Association for the Advancement 

 of Science. 



IRead before the Philosophical Institute of Canterbury, 2nd November, 



1898.] 



The complete mathematical discussion of earthquake move- 

 ment implies almost the whole range of the theory of elastic 

 solids, and this involves twenty-one constants, with equations 

 connecting them and their functions. A universal solution is 

 impossible, but some very general solutions of particular cases 

 have been obtained, and these can be applied in part to earth- 

 quake motion. This is particularly true in regard to moderate 

 earthquakes, or to the motion at some distance from the 

 origin. 



One very valuable law, for instance, discovered and proved 

 by Lord Kelvin, is that the most general form of small strain 

 may be resolved into two independent small strains, one of 

 which contributes dilatation and distortion without rotation, 



