1884.] Mr. Blanford on the Krakatoa Eruption. 55 



time of the initial disturbance at Krakatoa at 9 h. 32 min. A. m. (Local 

 mean time) . There does not appear to be any record of any marked 

 catastrophe at that hour, that which is especially noticed and described 

 by the Captain of the Charles Bal (in a letter published in Nature on the 

 6th December) having occurred at 11 h. 15 m. 



The Calcutta curve shows the first transit of the wave in a very 

 marked manner, viz., beginning at 11 h. 54 min. A. M. (Cal. mean time). 

 Now since the distance of Calcutta from Krakatoa measured on a great 

 circle is 33 d 11' or 2290 statute miles, an impulse starting from Krakatoa 

 at 9 h. 32 min. (L. T.), if travelling through an atmosphere at a tem- 

 perature of 80° with the velocity of the sound wave, would reach 

 Calcutta at 11 h. 21 min. (C. M. T.) If at the rate of 674 miles per 

 hour, computed by General Strachey from the intervals of the successive 

 transits of the East to West wave, it would reach Calcutta at 11 h. 

 48 min. (C. M. T.) which accorded very closely with the facts of the 

 record. 



The subsequent transits of the wave are not to be identified with 

 certainty in the Calcutta time. The second transit of the S. E. to 

 N". W. limb of the wave should occur about h. 51 min. A. M. of the 29th 

 but there is nothing very marked here on the trace. There is a distur- 

 bance nearly 4 hours earlier, viz., at 8 h. 36 min. p. m. of the 28th and a 

 less definite disturbance beginning at 4 h. 30 min. p. m. of the same day. 

 If this latter is the transit of the N. W. to S. E. limb of the wave, this 

 would be 32 h. 6 min. from its origin, having accomplished an arc of 

 326° 49' = 22569 statute miles. At this rate it would complete its re- 

 volution in 35 h. 22 min. which agrees fairly with General Strachey's 

 computed rate of progress for the West to East limb of the wave. It is 

 not improbable that the great Himalayan barrier which must be passed 

 by any wave sweeping from Krakatoa over Calcutta, or vice versa, seri- 

 ously interfered with the regular transmission of this portion of the 

 wave. 



Mr. Eliot thought that the barometric traces were very interesting 

 and afforded the clearest indication of the effect of the volcanic explo- 

 sion at Krakatoa. The disturbance which gave rise to such a wave, 

 which was propagated twice or thrice at least with visible effect on the 

 barometric column round the earth, must have been an enormous one, and 

 was probably the first outburst when the pent-up forces overcame the 

 resistance of the crust of the earth at the point of eruption. There was 

 one point to which Mr. Eliot wished to call attention, which was, that the 

 velocity of propagation of a wave due to a great disturbance of the air 

 was greater than that of an ordinary sound wave under similar condi- 

 tions of temperature, &c. Hence the assumption that the velocity of 



