HoGBEN. — On the Earthquake of December 5, 1881. 469^ 



the time-observations employed, gat an epicentrum situated 

 within tliat circle. 



2. By Time -observations. — Those used were — Eangiora, 

 7.33;- Greymouth, 7.33;- Westport, 7.34 ;- Sheffield, 7.34 ; = 

 Lyttelton, 7.36f;- Lyell, 7.35; Kumara, 7.35; Hokitika, 

 7.37 ; Christchurch, 7.37. The remaining times are either of 

 doubtful value, or are inconsistent with any possible theory. 



3. Method of Straight Lines (Milne, p. 200). — Four lines 

 are available — those got, namely, from the times at the follow- 

 ing pairs of places : (a) Eangiora-Greymouth, (b) Westport- 

 Shefiield, (c) Lyell-Kumara, (d) Hokitika-Christchurch. The 

 intersections of these lines give as possible positions of the 

 epicentrum the six points marked with dots on the map. 

 (d is one of the intersections of the last-named line, Hokitika- 

 Christchurch.) All the points except (d) are within the circle 

 C, and immediately to the north of Lake Sumner. The in- 

 tersection of (a) and (b) gives D, within a mile of F (see 

 below) . 



4. Method of Circles (Milne, p. 201). — I tried fourteen or 

 fifteen combinations of the given data, and the positions ob- 

 tained for the epicentrum are shown with small crosses on the 

 map. Most of these lie in the north-east quadrant of the 

 circle A. E is obtained from Lyttelton, Eangiora, Sheffield, 

 Greymouth, and nearly agrees with Westport. It corresponds 

 to a surface-velocity of six miles per minute, and a time at 

 the centrum of 7.23-| or 7.24 a.m. Its position is about 16 

 miles almost due north of the south-east end of Lake Sumner. 



5. Method of Co-ordinates (Milne, p. 206).— The most 

 satisfactory results are given by the first five of the times 

 named in Method 2. The equations give an epicentrum F, 10 

 or 104 miles north of the middle of Lake Sumner, 172° 16' 

 E. long., 42^ 34' S. lat. ; velocity, 7-18 miles per minute. 

 The equations show themselves not exact enough to determiiao 

 either the time at the centrum (they give 7.27J) or the depth 

 of the latter. By trial it is found, however, that a time at 

 the origin 7-26 a.m., and some depth less than ten miles 

 (perhaps less than five miles), will agree best with the position 

 and velocity found.! 



Intensity. — Whether we take F, E, or D, the velocity ap- 

 pears to have been very small — only 500ft. or 600ft. per 



* Most reliable. 



t The occiuTences reported to have been witnessed at Lake Sarah 

 (N.Z. Journal of Science, vol. i., p. 17G ; Trans. N.Z. Inst., vol. xv., 

 p. 5.33) can very well be explained as secondary effects of the earth- 

 quake. The statements of damage to the buildings, as far as they arc 

 opposed to our conclusion, can hardly weigh against the remaining evi- 

 dence. Indeed, the damage done to the south-east corner of the Castle 

 Hill Hotel suggests the transverse vibration of a wave proceeding from the 

 north-east — that is, from the epicentrum found. 



