O'Reilly — On Gaseous Products of Great Eruptions. 25 



the author of the report in question considers " that the volume 

 of the ejected gaseous substances was perhaps hundreds of times 

 as large " as that of the ashes. 



A similar calculation for the Tamburu eruption would give 

 us a proportionally greater volume of gases, and in both cases 

 merely terms of comparison, since, according to all the authors 

 who have had occasion to describe eruptions witnessed by them, 

 the quantities of gases and vapours emitted are great beyond all 

 comprehension. 



What, however, it is quite necessary to bear in mind, when 

 considering this question is that, simultaneously with the Krakatoa 

 eruption, gases and vapours were being emitted from a great 

 number of vents over the earth's surface — some mere hot springs, 

 from which the quantity of gas issuing, though continuous, is not 

 taken account of; others, volcanoes of every degree of activity and 

 violence, but only receiving attention when their violence is such 

 as to compel observation, but in totality representing a volume of 

 vapour and gas immensely greater than any estimate that can be 

 attempted, since no term of comparison nor any measurement is 

 at our disposal. 



It may naturally be remarked that I include both gases and 

 vapour, or steam, together, and that, according to the received 

 ideas, the steam was essentially furnished by the sea- water which 

 penetrated to the depths where the explosion originated. This is 

 not, however, by any means proved. It is to be remembered that 

 the amount of water held by the rocks, either chemically or phy- 

 sically, is estimated by Delesse to be much more than that of the 

 ocean, and this water may sometimes be brought into action. 

 But even admitting that all the water ejected as steam came 

 originally from the sea, the sudden transformation of such a 

 quantity of water into steam, and the sudden projection of such 

 quantities of it into the air, must have influenced both the sea 

 currents and the atmospheric currents, and in this way merit 

 being taken into consideration. But in eruptions, along with the 

 steam, or independently of it, gases are most certainly projected 

 into the air. That such were notably present in the Krakatoa 

 eruption is certainly stated by an eye-witness, a captain of one 

 of the vessels which happened to be in the neighbourhood, who 

 says "the presence of a powerful marsh gas was also easily 



