On Sea- Waves connected with a Japanese Earthquake. 583 



houses, throwing down stone walls, &c. It was reported 

 from there that an extraordinary fall or recession of the 

 sea preceded the greatest wave. No accurate observations 

 seem to have been made in those localities of the times and 

 the number of the prominent waves." 



The record at first shows a steady rise and fall of the water; 

 and it is not until 7h. 37 m. a.m. on June 15 that any change 

 occurs. There is then a small rise of about |- of an inch, the 

 first crest reaching the gauge at 7h. 43m. (?', e. at 6h. 15m. p.m., 

 G.M.T.). For about two hours this motion is somewhat irre- 

 gular ; but between 9h. 55m. a.m. and 5h. 8m. p.m. on 

 June 15 there is a group of. 17 waves with an average period 

 of 25tt minutes. The waves are all small ; they are most 

 marked between 9b. 55m. a.m. and lh. 40m. p.m. : and even 

 then the mean distance between crest and hollow of suc- 

 cessive waves is only 1*2 inches. The copy of the record closes 

 at 8 p.m. on June 17, when the surface of the water shows 

 signs of returning to its normal steadiness. 



The distance between the epicentre and Honolulu, mea- 

 sured along a great circle, is 3591 miles ; and, the time- 

 interval being 7h. 44m., it follows that the mean velocity 

 was 681 feet per second. If the ocean were of uniform depth 

 between the two points, the depth corresponding to this mean 

 velocity would be 14,492 feet. 



Sausalit'o (lat. 37° 51' N., long. 122° 29' W.).— Sausalito 

 lies at the entrance to San Francisco Bay. At the time of 

 the earthquake, the gauge here was the only automatic gauge 

 in operation on the Pacific coast of the United States. The 

 scale is "93 inch per hour for the horizontal coordinate (mea- 

 sured from the copy of the record), and 1 inch per foot for 

 vertical displacement. The time is the Pacific standard, that 

 of the 120th meridian west of Greenwich. 



In this, as in the Honolulu record, the first evidence of any 

 change is a rise (of 3*7 inches) in the level of the water *, 

 beginning at 12h. 53m. p.m. on June 15, the first crest reach- 

 ing the gauge at lh. 5m. p.m. (i. e. at 9h. 5m. p.m. G.M.T.). 

 During the first two hours, the waves are larger and of lono-er 

 period than those which follow, the chief movement beino- 

 between lh. 30m. and lh. 45m. p.m., when the water rose 

 6*8 inches and fell 2'2 inches. After this, they become more 

 regular. Between 3 and 6 p.m. there are 30 waves, with an 

 average period of 6 minutes and a mean distance between 



* It should be noticsd that at two Japanese stations, Ayukawa and 

 Hanasaki-mura, the first movement was a fall in the level of the water. 

 Nature, vol. liv. p. 449 (1896). 



