274 PROCEEDINGS OF SECTION A. 



the various meteorological stations, principall)' in the north and 

 north-east of Tasmania and on the islands between Tasmania and 

 the mainland. For this purpose he issued instructions to the 

 various observers as to the consistent use of the adjectives " very 

 slight," " slight," " heavy " or " severe," and "very severe." In 

 a large mimber of instances sufficient details are given to enable 

 me, especially after discussing the matter with Captain Shortt, to 

 assign valvies, on the Rossi-Forel scale, to each of his adjectives. 



The result of the steps taken is a most valuable catalogue of 

 the shocks. Unfortunately the time observations were not exact 

 enough, except in one or two cases, to enable us to ascertain the 

 origin thereby ; but an earthquake that occurred on the 27th 

 January, 1892, can be referred to a definite origin; and I hope to 

 examine many of the shocks of the years 1883-6 as to the possi- 

 bility of their having come from the same spot. 



The table appended gives the number of shocks for each 

 month from April, 1883, to December, 1886, arranged according 

 to intensity, on the Rossi-Forel scale, and the total intensity per 

 month in absolute units. 



[Note. — It will be observed that no shocks are classed as IV. 

 This does not mean that no shocks of that intensity Avere felt, but 

 indicates some difficulty in assigning the exact degree for a large 

 number of shocks between III. and V. I tried several hypotheses 

 agreeing with the available evidence, but all came to nearly the 

 same result, namely, that there were 2,210 shocks varying from III. 

 to v., and their total intensity was a little less than 160,000 units. 

 The shocks that might therefore be classed as IV. are put down as 

 III. or v., according as the evidence inclines to one or the other 

 degree of the scale.] 



The total number of shocks for the forty-five months was 2,540, 

 an average of 56-4 per month, which would be sufficiently startling 

 were it not that the average intensity of shock was only between 

 III. and IV. One month — October, 1883 — enjoys the questionable 

 distinction of having 231 shocks recorded against it, that is, seven 

 or eight shocks a day ; and November of the same year is not far 

 behind. The total intensity was 186,690 units, or about nineteen 

 times acceleration due to gravity, which gives an average intensity' 

 per shock of 73*5 millimetres per second. If all this were concen- 

 trated into one instant it would give an impulse of 612ft. per 

 second. 



[The minimum value assignable for the average intensity of 

 shock is 68"3, a figure that allows also for the possibilities of error 

 introduced by classifying shocks of intensity IV. as III. or V. 

 The mean of '73-5 and 68-3 is 70-9 units, which we may take to be 

 the average intensity of the shocks felt.] 



The diagram accompanying this paper (Plate VII.) shows, in a 

 graphical form, the history of the series of shocks ; the ordinate of 

 any point on the curve shows the total intensity Der month in 



