A GREEN SUN AND ASSOCIATED PHENOMENA. 401 



Krakatao to Mauritius, 161 miles per hour. 



,, Cape Coast Castle, 71 „ 



„ Trinidad, 74 „ 



Near Honolulu, lat. 8° 21' N., long. 155° 28' E., 85 



These are the velocities if we assume that the column of dust was sent up 

 by the great explosion which took place between 8 a.m. and 9 a.m. on the 27th; 

 and even the plutonists seem to hesitate to affirm that the violence of the 

 previous explosions was sufficient to send the dust up to the required height, 

 though the first great shower of dust must have been ejected some time 

 previous to that hour. When we consider that, from the nature of the case, the 

 deduced velocities can only be very rough approximations, being in each case the 

 minimum value, it must be admitted that the more distant ones agree fairly 

 well with each other. Here, however, we are met by two difficulties, viz., is 

 there any reason to believe in the existence of an upper current moving with 

 anything like the requisite velocity? and, if it moved so fast along the one 

 track, how was it so long of reaching Southern India"? Regarding the first of 

 these difficulties, it seems absolutely certain that no such uniformly strong 

 currents exist, at least at any altitude to which the dust could possibly have 

 been projected. Mr Lockyer attempts to overcome the second difficulty by 

 assuming an upper current from east to west, nearly along the equator. It 

 crossed to the north however to reach Cape Coast Castle and Trinidad— and 

 an under current from south to north. If, however, Mr Manley's observations 

 are accurate, as there seems every reason to believe they are, it appeared at 

 Ongole as soon as in Colombo, and at least twelve hours sooner than in 

 Madras; and, if the Belgaum observations are accurate, it appeared there a day 

 before it was seen in Colombo. Taking, however, only those observations about 

 which there can be no doubt we get the following velocities, taking the shortest 

 lines between Krakatao and the various stations : — 



To Colombo, . . . 2000 miles, 67 miles per hour. 



„ Madras, . . . . . 2240 „ 7*3 

 „ Bellary, .... 2450 „ 7 9 

 Lat. 10° 4' N., long. 64° 12', 3100 „ 9-8 



velocities increasing with the distance from the source. 



Taking these along with the Japan observations, which require a velocity 

 of over 40 miles per hour, it seems very difficult to believe that dust would 

 have travelled in these different directions with such very different velocities. 

 Finally, we have the negative evidence, which in this case seems to have some 

 weight, that the first rain which fell after the appearance of the green sun 

 contained no volcanic dust. I collected several gallons of the rain which fell 

 on the night of the 29th, and had the sediment which it contained carefully 



