4?08 On the Get/sirs of Iceland. 



always supposed that its temperature there was that of boiling 

 water; the second and third experiments show, in fact, that 

 at one metre below the surface it is so. Lastly, a thermo- 

 meter placed at the bottom of the channel during an erup- 

 tion, indicated a temperature of 115° C. 



We see that the column of the water of the Strokkur pos- 

 sesses, at different heights, much more constant temperatures 

 than those of the Geysir, and that the influence of the erup- 

 tions is very little felt; this depends evidently on the con- 

 tinual boiling of the water, which determines incessantly 

 ascending currents in the column and a sort of intermixture. 

 The mean height of the column of water of the Strokkur is 

 equal to a column of mercury at 0°, of 0'"-7179. 



The temperature at which the water, submitted to this pres- 

 sure and to that of the atmosphere, would begin to boil, is 

 120''04<3. 



We have seen that the maximum temperature at the 

 bottom of the Strokkur was 115°; the difference between this 

 maximum and the point of ebullition of the water is therefore 

 5°*043. This number is sensibly smaller than the corre- 

 sponding number found at the Great Geysir, which may be 

 owing to the point attained by the thermometer in the Strok- 

 kur being nearer to the subterranean source of heat, or to the 

 channels which form the communication between the liquid 

 column and that central point being narrower ; the heat parted 

 with by the vapour condensed to the water of this channel is 

 transmitted more rapidly to the base of the column. 



The eruptions of the Strokkur, which are quite as high as 

 those of the Great Geysir, instead of presenting, like the 

 latter, the appearance of a beautiful fountain with a base three 

 metres in diameter, and a crown of about eighteen metres, 

 present only an ensemble of sharp, jagged points, resembling 

 very tall and slender yew-trees. In the Geysir, the eruptions 

 always take place naturally; at the Strokkur, on the contrary, 

 they are either natural or artificial. All travellers in fact 

 have remarked that, if the orifice of the Strokkur is filled 

 with light stones or pieces of earth and grass, the oscillations 

 of the water cease for some instants ; then, at the end of five 

 or ten minutes, a jet of a blackish water charged with earth 

 is shot out to a great height, and is followed by other inter- 

 mitting jets during eight to ten minutes. This experiment, 

 which can be repeated several times a day with success, seems 

 to prove that the small excess of pressure resulting from the 

 accumulation of clods of earth upon the water suffices to 

 hinder the normal disengagement of the vapour through 

 the column of water, and to augment the tension of that which 



