Presents. 



253 



3400 miles, and for Port Elizabeth, in South Africa, distant 5450 

 miles ; that the same value should be obtained for two places, one of 

 which is 2050 miles further from the origin than the other, shows 

 that there is not likely to be any gross error in the time adopted for 

 the starting of the wave from Krakatoa ; the value is, moreover, 

 interesting in that it is practically identical with Airy's velocity of a 

 free tide-wave over an ocean 15,000 feet deep, which is approximately 

 the depth of the ocean on this line ; in other directions the velocities 

 are less, namely, towards Gralle, 397; Negapatam, 355; and Aden 

 371 miles. In the calculations the velocity has been assumed 

 uniform in each instance, as a matter of convenience, but it must 

 in reality have been greatest wherever the ocean depth was 

 greatest. The greatest depth is known to occur on the lines to 

 Ports Louis and Elizabeth, for which we have the greatest velo- 

 cities ; but the wave which impinged on the Indian stations, and 

 eventually reached Aden must for a considerable portion of its 

 course have been identical with the wave which impinged on Ports 

 Louis and Elizabeth, and then it must have travelled with the same 

 high velocity; afterwards, on passing over shallower oceans, its 

 velocity must have been materially retarded, and may have fallen 

 much below the averages, 355 to 397 miles, for the whole course. 

 This appears probable, moreover, from the evidence of the earthquake 

 in the Bay of Bengal on the 31st December, 1881, of which an 

 account — communicated by myself — was published in the "Proceed- 

 ings of the Asiatic Society of Bengal " for March, 1883. The 

 position of the centre of impulse has been fairly well fixed at a point 

 nearly on the line between Port Blair and Negapatam, and the time is 

 known within a few minutes. The supertidal waves caused by this 

 earthquake at the contiguous tidal stations much exceeded in magni- 

 tude the waves caused at the same places by the eruption at Krakatoa, 

 but their velocity was found to range between 240 and 120 miles an 

 hour, varying with the general depth of the water traversed and the 

 configuration of the foreshore at the respective stations. It is pro- 

 bable, therefore, that for the latter portion of its course the wave from 

 Krakatoa to the same stations travelled with no greater velocity than 

 on the occasion of the earthquake in the Bay of Bengal. 



Presents, December 6, 1883. 



Transactions. 



Baltimore : — Medical and Chirurgical Faculty of the State of 

 Maryland. Transactions. 85th Session. 8vo. Baltimore 1883. 



The Faculty. 



Geneva : — Institut National Grenevois. Bulletin. Tome XXV. 8vo. 

 Geneve 1883. The Institute. 



