28 Scientific Proceedings, Royal Dublin Society. 



cold springs, which may be considered as bearing some relation to 

 the total volcanic activity. 



The oil-springs of America and of the Caspian must be con- 

 sidered as coming into this category, since, by their constitution, 

 they are akin to certain of the gases which accompany volcanic 

 action, and nothing yet absolutely proves their organic action. 



With this continuous emission of gases and steam must in 

 some way be connected the slow movements of the earth's surface, 

 which are now being more attentively studied than had been the 

 case ; and did we posses sufficient data in respect of these emissions 

 in toto, it might be possible to foresee the recurrence of volcanic 

 eruptions, or of earthquakes, and of disturbances of the earth's 

 surface. Still more important is the bearing of this total emission 

 of gases and vapour on the question of the radiation of earth heat 

 into space. As the points from which the gases come are certainly 

 situated at relatively great depths, and in the case of such eruptions 

 as that of Krakatoa most certainly at a very great depth, the surface 

 radiations must be considered as forming part of a total radiation, 

 some terms of which correspond to points deep in the interior of 

 the earth. That the seat of the great explosion of Krakatoa was 

 very deep may be inferred from at least two facts — the one, that 

 the " recoil" (to use the expression) of the explosion was felt at or 

 near the antipod of that point, as observed by Monsieur Forel in 

 Nature, March 26, 1885. He states that underground noises were 

 heard at Caiman-Brae, in the Caribbean Sea, in August, 1883, 

 contemporaneously with the eruption, the exact antipod of Krakatoa 

 being the middle of the State of Colombia, on the Magdalena river, 

 between the towns of Antigua and Tunja. 



Another fact which would lead one to infer that the seat of the 

 explosion lay very deep was, that the island was split according to 

 an east-to-west direction, so that the whole northern part became 

 detached, and sank to a depth of 200 m., or more. " In the place 

 where the fallen part of Krakatoa once stood there is now every- 

 where deep sea, generally 200 m. — in some places even more than 

 300 m. deep " (Nature, vol. xxx. p. 12). Now this splitting in an east- 

 to-west direction may perhaps be considered as the result of the 

 lateral pressure and intense friction of the solid matter, when being 

 ejected, against the west side of the vent, since coming from a 



