330 
the circle where the tremor should be felt at the same 
instant, just as a ripple from a stone thrown into a pond 
progresses all round from the centre outwards.” Of course, 
difference of conductivity in different strata would tend to 
distort, more or less, the supposed circle; still, overlong dis- 
tances, I think we may fairly assume a pretty nearly equal 
average in different directions. 
In applying this principle, it was necessary to first 
“ smooth” the time curves, by averaging the different time 
reports from contiguous localities (I had 54 to work upon). 
I now quote from the article referred to (22 July):— 
“Tt would appear that the wave first struck the coast 
line of N.S. Wales, from Sydney to Eden, nearly simul- 
taneously, at 2 p.m. (1°44 p.m. our time). It next reaches 
Ringarooma at 1:55. A nearly synchronous line next passes 
through Wilson’s Promontory, George Town, Launceston, 
Midland, Hobart, and the Huon, at 1°57. Lastly, it reaches 
Bischoff at 2-1. Now, the nearest focus ican find for these 
synchronous curves is about the Hast Coast of New Zealand. 
Setting one leg of a pair of compasses upon Mount Hgmont, 
the other leg would strike these curves with considerable 
accuracy. These curves are separated by a distance of about 
260 miles (roughly) from inner to outer. An earthwave has 
been estimated to travel at from 1200 to 1800 miles per hour. 
The shock reached Sydney 17 minutes before it reached 
Bischoff. This, at 20 miles per minute, would give 340 miles. 
But I think we have good reason for estimating the progress 
of the wave at a much slower rate, imasmuch as nearly alk 
reports agree in describing the sound as preceding the shock, 
showing that the earth wave was slower than the sound wave. 
Taking this circumstance into account, I think the time 
taken in passing from curve to curve is not inconsistent with 
the foregoing hypothesis.” 
In this analysis I am, of course, not responsible for the 
correctness of the data, only for the conclusions deduced 
therefrom. 
Next in importance, both as to strength of shock, and also 
with regard to the area over which it is traceable with 
reasonable precision, is that of 19th September last. Apply- 
ing the same principles of investigation as before, it would 
appear that this wave first reached the N. Hast Coast at 
about 8°30 p.m.; then Launceston at 8374; Longford, 
Corners, Campbell Town, and Ross, at 8:38; and Prahran 
and Cape Schanck, at 8°39 (our time). A synchronous curve 
of 8:39 would pass through Prahran, Cape Schanck, and 
George Town,—a little west of Launceston, by Campbell 
Town, and somewhat east of Hobart. The focus of such a 
