156 Intelligence and Miscellaneous Articles. 



exerting an immense mechanical force. By an easy calculation it 

 might be shown that the heat thus stored up could generate, under 

 ordinary atmospheric pressure, a column of steam having a section 

 equal to that of the tube and a height of nearly thirteen hundred 

 yards. This enormous force is brought into action by the lifting 

 of the column and the lessening of the pressure described above. 



A moment's reflection will suggest to us that there must be a 

 limit to the operations of the Geiser. When the tube has reached 

 such an altitude that the water in the depths below, owing to the 

 increased pressure, cannot attain its boiling-point, the eruptions of 

 necessity cease. The spring however continues to deposit its silica 

 and forms a laug or cistern. Some of these in Iceland are of a 

 depth of thirty or forty feet. Their beauty is indescribable ; over 

 the surface a light vapour curls, in the depths the water is of the 

 purest azure, and tints with its own hue the fantastic incrustations 

 on the cistern walls ; while at the bottom is observed the mouth of 

 the once mighty Geiser. There are in Iceland traces of vast, but 

 now extinct, Geiser operations. Mounds are observed whose shafts 

 are filled with rubbish, the water having forced a way underneath 

 and retired to other scenes of action. We have in fact the Geiser 

 in its youth, manhood, old age, and death, here presented to us : — 

 in its youth as a simple thermal spring, in its manhood as the erup- 

 tive spring, in its old age as the tranquil laug, while its death is 

 recorded by the ruined shaft and mound which testify the fact of its 

 once active existence. 



Next to the Great Geiser the Stokkur is the most famous eruptive 

 spring of Iceland. The depth of its tube is forty-four feet. It is 

 not however cylindrical like that of the Geiser, but funnel-shaped. 

 At the mouth it is eight feet in diameter, but it diminishes gradually, 

 until near the centre the diameter is only ten inches. By casting 

 stones and peat into the tube and thus stopping it, eruptions can be 

 forced which in point of height often exceed those of the Great 

 Geiser. Its action was illustrated experimentally in the lecture, by 

 stopping the galvanized iron tube before alluded to loosely with a 

 cork. After some time the cork was forced up and the pent-up 

 heat converting itself suddenly into steam, the water was ejected to 

 a considerable height ; thus demonstrating that in this case the tube 

 alone is the sufficient cause of the phenomenon. 



XXI. Intelligence and Miscellaneous Articles. 



ON THE CONDENSATION OP GASES AT THE SURFACE OF SOLID 

 BODIES. BY MM. J. JAMIN AND A. BERTRAND. 



IN the various experiments intended to establish the physical theory 

 of gases, it is implicitly supposed that their state of equi- 

 librium is not influenced by the walls of the vessels in which they 

 are contained ; it is supposed that no attractive or repulsive force 

 exists between solid and gaseous molecules. Nevertheless the general 

 principles of molecular physics do not justify our thinking that this 

 can be the case ; we have no reason to suppose that gases are de- 

 prived of a property so energetically manifested by liquids ; and if it 



