TIDAL AND LEVELLING OBSERVATIONS. 205 



2. This negative wave was succeeded by a great positive wave at 



an interval ranging from 75 minutes at Negapatam, the 

 station nearest Krakatoa, to 24 minutes at Aden, the most 

 distant station. 



3. Super-tidal wavelets, denoting antecedent minor eruptions, 



were registered at the whole of the Indian stations some 

 hours, more or less, before the effects of the great eruption. 

 This shows that the explosions were at first comparatively 

 faint and feeble, being felt only at the nearest stations, but 

 afterwards they increased in intensity, becoming sensible 

 even at the most distant station three hours before the effects 

 of the great eruption. 



4. Great super-tidal waves of amplitudes ranging from a maximum 



of 22 inches at Negapatam to a maximum of 9 inches at 

 Aden were registered at all the stations which were in a 

 position to receive the full force of the eruptions at Krakatoa, 

 unobstructed by the configuration of the foreshore. Other 

 waves of less magnitude occurred at these stations at 

 intervals of one to two hours for about 12 hours after the 

 first great wave. 



5. The secondary great waves were succeeded by wavelets 



gradually diminishing in size but continuing for some time. 



6. Loud reports resembling the firing of distant guns were heard 



at Port Blair and in the Nicobar islands on the 26th and 



27th August, and, being supposed to be signals from a vessel 



in distress, a steamer was sent out in search of the vessel. 



Similar reports were heard at two places on the coast of 



Ceylon on the 26th, first at 6 p.m. and afterwards at 



midnight. 



These facts show that the terrible and disastrous eruption at 



Krakatoa, which 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 4,000 miles.* 



The spirit-levelling operations carried on in connexion with the 

 tidal operations in 1882-83 completed the last link in the long line 



* General R. Straehey, R.E., C. S.I. , lias communicated an interesting and suggestive 

 note to the Royal Society on the barometrical disturbances which passed over Europe 

 between the 27th and 31st August, and investigated the speed of the barometrical 

 vives travelling from Krakatoa round the earth. 



