Volcanos and Earthquakes, 79 



yet, on the other hand, we must consider, that when the vapour, 

 which had not yet attained its maximum of expansive force, has 

 effected an elevation, then, a regressive effect, as regards dura- 

 tion of time, will ensue, because, by the elevation, the space 

 which confined the vapour has become enlarged. Secondly, if 

 the conducting power of the solid mass be greater than we have 

 just assumed it to be, then the heat, which is communicated to 

 the surface of contact by condensation of vapour, is as quickly 

 diffused above, as it can be conveyed from the vapour below, 

 and if the latter produce a continued elevation, the effect must 

 inevitably be regressive. We can therefore conceive it possible, 

 under the conditions stated, that the same force, viz. vapour of 

 water, which, when in contact with a fused mass, developes its 

 whole intensity in a short time, can produce only a gradual 

 effect, when in contact with solid masses whose temperature is 

 far below that of the vapour. We thus see the possibility of 

 fused masses being raised by vapour in a short time, while solid 

 masses may be raised very slowly by the same agent, and that 

 the latter elevation may go on in a regressive ratio. Lastly, 

 it is even possible that a gradual elevation of a solid mass may 

 continue, although the elevating effect of the vapour has long 

 ceased. For instance., if the subterraneous heating by steam 

 continue, and if the heat, communicated to the surface of con- 

 tact by condensation of the vapour, be diffused above more 

 slowly than it is conveyed below, then it is clear that the solid 

 mass supported by the vapour, will gradually be expanded. 



These remarks have shewn that the operations of vapour, as 

 an elevating force, may be very various as regards the relations 

 of time and space, and that its effects depend not only on its 

 own temperature, but also on that of the masses it has to ele- 

 vate, on their relative conducting power, and lastly, on the ca- 

 pacity of the space within which its operations take place. 



We can therefore understand how the slow elevation of Scoiv- 

 dinavia may be a result of the operation of watery vapour, ta- 

 king place in a diminishing ratio, and how therefore this phe- 

 nomenon stands in close connexion with the original elevation 

 of that country, which is principally composed of masses of ig- 

 neous origin. We shall pass over the consideration of the 

 question, whether this original elevation took place in a fluid or 



