26 



Scientific Proceedings, Royal Dublin Society. 



detected." — Nature, vol. xxix. p. 29. Moreover, from the obser- 

 vations of Fouque at Santorin, and of St. Claire Deville at 

 Vesuvius, we know that hydrogen occurs as one of the emitted 

 gases. The following is a Table given by Fouque, p. 227 of 

 his work on Santorin, of the gases collected on the 17th March, 

 1877, at that place : — 



It must further be remembered, that very frequently, previous to 

 eruptions of active volcanoes, gases are emitted from the craters 

 and cracks of the volcanoes, and that the emission continues long 

 after the cessation of eruptive activity, and may continue for 

 centuries when the volcano passes into the state of a hot spring. 

 Finally, all over the world, both on land and in the ocean, as has 

 been already remarked, this emission is going on continuously 

 from the active volcanoes, the hot springs, and simple jets of gas, 

 and the daily total of this quantity of gas must be something 

 past all calculation. 



It may be objected that were there such continuous additions 

 being made to our atmosphere, Science would already have ascer- 

 tained the fact by comparative barometric observations. But it must 

 be remembered that such barometric observations should embrace 

 the whole earth's surface, and have been recorded for a sufficiently 

 long time to allow of any effective comparison — that the observa- 



