264 



have been tabulated and arranged. Altliougli it would be useless 

 to attemj)t to reproduce all the reports, yet it seems desirable 

 to bring a short abstract of them before the Eoyal Society 

 as the chief scientific body in Tasmania, so that members and 

 others may be put in possession of what has really hap- 

 pened, and of the results which may be fairly deduced from 

 the observations. It is hoped that interest in these observa- 

 tions may be thus stimulated, so that any shochs which 

 occur in the future may be " more carefully observed and re- 

 corded, and we may hope that in time many of the cjues- 

 tions which remain for solution may be satisfaccorily 

 answered, and others on which one has to speak with great 

 caution may be completely established. 



Before discussing reports received it may be well to state 

 briefly the direction in which our enquiries and observations 

 should be made, and what we may fairly hope to learn by 

 careful observation. 



In the first place we can hope to learn little as to the 

 causes of earthquakes. With these, although a fertile field of 

 controversy for those who delight in it, we, as observers, have 

 little to do, and therefore they will only be alluded to briefly 

 at the end of the paper. 



But there are many problems awaiting solution to which 

 we may devote our attention. Thus we ought to try and 

 find the point directly above the disturbance which causes 

 the earthquake, and from which the " seismic vertical " passes 

 down to that centre. Then to find the directions in which 

 the shock travels out from the centre, and the places at 

 which it arrives simultaneously, so as to determine the co- 

 seismic lines, and whether they are circles, ellip>ses, or cjuite 

 irregular. To observe the rate at which the wave of dis- 

 turbance travels ; whether the rate varies in passing through 

 different descriptions of rock, and if so, by how much. 



If it is ever reflected or thrown back at the junction of 

 dissimilar rocks, 



To determine, if possible, the angle at which the vibration 

 reaches the surface of the ground at different places, and 

 thence to calculate the depth of the disturbance and length 

 of the seismic vertical. 



Then the exceedingly important and difficult problem 

 whether any change ni the level of the ground has accom- 

 panied or followed the earthquake, and if so, whether the 

 change, either elevation or depression, is permanent. Again, 

 whether the shock has been felt equally at all places in the 

 same neighbourhood, and if not, what determines the 

 difference. 



These are some of the points on which we may hope to 

 obtain information, but there are others which can be 



H 



