HoGBEN. — The Tasmanian Earthquake. 595 



tion, I was led to reject all the times from Tasmania except 

 those of Hobart and Launceston. These I place in the first 

 class, as comparatively good times; one or two others — e.g., 

 St. Mary's, Eagle Hawk Neck, Branxholm, and Campbell- 

 town — are probably within about a minute of the true time, 

 but not exact enough to be relied upon, or to be classed with 

 ■ Hobart and Launceston. 



One thing is clear from the reports from the various 

 Tasmanian observers — namely, that the earthquake was a 

 compound one, consisting of four (or perhaps five) shocks, three 

 near together (Captam Shortt gives 2.48, 2.49, and 2.50 at 

 Hobart) and one about seven or eight minutes later. In 

 other respects besides the time — as regards the intensity and 

 direction of the shocks — much valuable information can be 

 gleaned from these reports, and there is a general agreement 

 m the conclusions to which they point. 



The Victorian returns are eleven in number. The times 

 are shown by the normal equations to be inferior in value to 

 the times for Hobart and Launceston ; I have accordingly not 

 put any of them in the first class. Two of the times, hovv^- 

 ever, may be assigned to the second class — Wilson's Pro- 

 montory (2.49i) and Sorrento (2.51^). These, with Bairns- 

 dale, are set down in Mr. Ellery's list as the most reliable of 

 the Victorian times. Bairnsdale must be rejected unless it 

 refers to the last of the four shocks ; even then it is probably 

 two or three minutes out. It may be remarked that Mr. 

 Ellery expresses a fear that the times from Victoria are not 

 exact enough for use in calculations of the origin. Only 

 four times were received from New South Wales ; three of 

 these are fairly good, and must be put in the first class. The 

 other— Green Cape(2.56|) — would probably be correct for the 

 last shock. 



The second shock was the chief one, and the one noticed 

 most by ordinary people. At several places where the first 

 three shocks were felt their character was clearly distinguished. 

 I propose briefly to discuss the earthquake under the heads — 

 (I.) Origin of shock ; (II.) velocity of propagation ; and (III.) 

 intensity of shock. 



(I.) For the purpose of finding the epicentrum, or point on 

 the earth's surface immediately above the origin of the dis- 

 turbance, we may use — {a) the directions observed at the 

 various places ; (6) the times of beginning, or any other 

 marked phase of an earthquake ; or (c) the degree of the 

 intensity of the shock as felt at different places. Of the 

 various methods, those depending on good times — (&)— are by 

 far the best, and the indications given by the impressions or 

 observations of direction are the least reliable. I am, how- 

 ever, very far from holding with Mr. Biggs that they are 



