TASMANIAN EARTH TREMORS. 259 



source or focus. These questions the author discusses at 

 considerable leng-th, detaiUng his various experiments and 

 apparatus, by which he proves that the popular notion as to 

 the magnitude of the earth motion is a very greatly 

 exaggerated one, and that personal impressions are wholly 

 unrehable, owing probably to our natural sensitiveness to 

 vibration. With regard to the second question, the author 

 infers that our impressions are no more to be trusted as to 

 the direction of motion than as to its magnitude. Further, 

 that mere local apparatus, however perfect, is not to be trusted 

 in this respect, as it can only record the molecular motion, 

 which is quite distinct from the wave progression. The only 

 reliable means of determining the direction of the lines of 

 progression, and, from their convergence, the focus of the 

 disturbance, is by finding the synchronous curves from an 

 analysis of the times at which the shock is felt in different 

 localities, or, under favourable circumstances, by the direction 

 of the sound. It is assumed that the earth-wave progresses 

 in a more or less irregular expanding circle, just as a ripple 

 from a stone thrown into a pond progresses all round from 

 the centre outwards. 



The apphcation of this principle was, however, rendered 

 difficult in our case by the unreliability of the times as 

 reported, and in most cases the limited range embraced by 

 the reports. The three greatest shocks were those of the 

 13 July and 19 September, 1884, and 10 May, 1885. The 

 result of the analysis of each of these was to locate the focus 

 far away to the eastward in the direction of and near to New 

 Zealand, — a result quite contrary to the popular notion and 

 e\e\\ to the author's preconceived ideas. The subsequent 

 violent outbreak in New Zealand, however, gave strong 

 countenance to the conclusion arrived at. 



In the author's opinion our tremors are, at least to a 

 large extent, merely the sympathetic vibrations from violent 

 disturbances in distant localities, in illustration of which a 

 lengthy table is given of closely approximate coincidences of 

 many of our important tremors with violent shocks elsewhere. 

 The author has failed to find any apparent connection 

 between our tremors and either barometric fluctuations or 

 lunar phases or positions. 



