1884.] Tidal Disturbances caused by Eruptions at Java. 251 



heard at two places on the coast of Ceylon on the 26th, first at 6 p.m. 

 and afterwards at midnight.* 



These facts show clearly that the terrible eruption at Krakatoa, 

 which carried desolation over the surrounding regions and was 

 attended with such an appalling loss of life, was preceded for some 

 hours by minor eruptions which were insignificant only by comparison, 

 for they produced effects which were sensible even at Aden, a distance 

 of upwards of 4000 miles. It is possible, therefore, that some at 

 least of the subsequent supertidal waves may be due to eruptions 

 occurring subsequently to the great eruption. 



It is a singular fact that we are still without any precise and definite 

 information of the time at which the great eruption took place. In 

 a very interesting and suggestive note on the Barometrical Disturb- 

 ances which passed over Europe between the 27th and 31st August — 

 communicated to the Hoyal Society on the 12th December — General 

 Strachey gives an investigation of the speed of barometric waves 

 travelling from Krakatoa round the earth, some from east to west, 

 others from west to east, and he estimates that the great disturbance 

 which caused the initial barometric rise probably occurred at 9 h. 24 m. 

 local time on the morning of the 27th August. Now Major Baircl 

 shows that the primary effect of the great eruption was to 

 produce a recession or fall of the sea-level at each of his tidal 

 stations, and this was also noticed at the Mauritius. It seems 

 probable that the initial barometric rise occurred at the same time 

 as the initial oceanic fall or great negative wave, which is shown to 

 have preceded the first great positive wave by an interval ranging 

 from 75 minutes at the nearest Indian station to " about a quarter of 

 an hour" at the Mauritius. Major Baird has ascertained from Her 

 Majesty's Consul at Batavia that the first great positive wave reached 

 Batavia at 12 h. 10 m. mean local time on the afternoon of the 

 27th August ; he infers from the table of the velocities of free 

 tide waves in Sir George Airy's article on Tides and Waves in the 

 " Encyclopedia Metropolitana," that as the distance from Krakatoa 

 to Batavia is about 105 miles, and the average depth of the sea 

 between them 186 feet, the wave must have taken about two hours to 

 travel that distance. Thus, allowing five minutes for difference of 

 longitude, the local time of the occurrence of the first great positive 

 wave at Krakatoa would be 10 h. 5 m. a.m., or about 1 h. 40 m. 

 later than General Strachey's estimated time of the initial baro- 

 metric rise. If, however, we assume this time to have been 

 identical with that of the initial oceanic fall, and to have preceded 

 the first great positive wave by an interval somewhat greater at 



# The times throughout Major Baird's report are referred to the meridian of Port 

 Blair, in lat. 11° 41' N., and long. 92° 45' E. of Greenwich, the easternmost tidal 

 station at which the tides were disturbed. 



