598 Transactions. — Chemistry and Physics. 



more exact. The time I have taken is that of the beginning- 

 of the second shock (or maximum). The times in Class I. 

 are: Launceston, 2.48|- a.m.; Hobart, 2.49 a.m.; Kiama, 

 2.52|- a.m.; Kiandra, 2.52^ a.m.; Bombala, 2.49^ a.m.: all 

 Hobart mean time. 



For Launceston I had three returns : Mr. A. B. Biggs, 

 2.48^; Captain Shortt, 2.49 ; Professor Liversidge, 2.48. The 

 time sent to Captain Shortt is noted as probably not quite at 

 the begmning, so it is a little too late ; that given by Professor 

 Liversidge is probably too early — there vpas a little delay in 

 finding the matches, and allowance made for such delay 

 during an earthquake is generally rather too great. Mr. Biggs 

 took the time by a chronometer at once. All the times were 

 verified as soon as possible afterwards by standard time. I 

 think we may say, in taking 2.48^ as the right time, we are 

 correct to the nearest half-minute. At Hobart three shocks 

 were noted — two slight and one sharp. Three were also noted 

 at Carnarvon and other places, and in each case the middle 

 shock — that is, the "second" shock referred to above — was 

 the severe one : Hobart, therefore, 2.49. Great care seems 

 to have been taken in checking the New South Wales times, 

 and they are at least correct to the nearest minute. 



The times which at first I placed in Class II. were : 

 Glenora, 2.51 ; St. Mary's, 2.49^ ; Eagle Hawk Neck, 2.49 ; 

 Fingal, 2.50; Branxholm, 2.47; Campbelltown, 2.47^; Sor- 

 rento, 2.51-1 ; "Wilson's Promontory, 2.49^. 



Method of Co-ordinates. — After some preliminary trials by 

 the methods of straight lines''' and circles, I formed the equa- 

 tions of observation for all the places in Classes I. and II. 

 as in Milne's "Earthquakes," p. 206, and then the normal 

 equations from them (see " Merriman's Method of Least 

 Squares," chap. iii.). No good result was obtained, however ; 

 but the conclusion could plainly be drawn that the times in 

 Class II., being more or less inconsistent with one another, 

 were less reliable than those of Class I. 



The weights assigned for the several observations were : 

 For Hobart, 25 ; for Launceston, 16 ; Kiama, 9 ; and for the 

 rest, 4, 2, or 1. 



I then returned to the method of circles, which, with data 

 of the kind we have, and for an earthquake whose origin is 

 not near any of the places of observation, is as good as the 

 method of co-ordinates. Cjo is the epicentrum obtained by 



* S was obtained by the method of straight lines from the two pairs, 

 Kiama-Kiandra (2.52^), Hobart-Launcestou (2.48J). It corresponds to a 

 surface-velocity of a/bout twenty-six miles per minute. Subsequent com- 

 parison of the records, however, for reasons already given, led me to 

 believe that 2.49 was the true time for Hobart, or as near as we could get 

 to it. S remained as a rough first approximation. 



