154 Royal Institution. 



The lining of the tube is silica, evidently derived from the water \ 

 and hence the conjecture may arise that the water deposited the 

 substance against the sides of the tube and basin. But the water 

 deposits no sediment even when cooled down to the freezing-point. 

 It may be bottled up and kept for years as clear as crystal, and 

 without the slightest precipitate. A specimen brought from Iceland 

 and analysed in this Institution was found perfectly free from sedi- 

 ment. Further, an attempt to answer the question in this way would 

 imply that we took it for granted that the shaft was made by some 

 foreign agency and that the spring merely lined it. A painting of the 

 Geiser, the property of Sir Henry Holland — himself an eyewitness 

 of these wonderful phenomena, — was exhibited. The painting, 

 from a sketch taken on the spot, might be relied on. We find here 

 that the basin rests upon the summit of a mound; this mound is 

 about forty feet in height, and a glance at it is sufficient to show 

 that it has been deposited by the Geiser. But in building the 

 mound, the spring must also have formed the tube which perforates 

 the mound ; and thus we learn that the Geiser is the architect 

 of its own tube. If we place a quantity of the Geiser water in 

 an evaporating basin, the following takes place : in the centre the 

 fluid deposits nothing, but at the edges where it is drawn up the sides 

 of the basin by capillary attraction, and thus subjected to a quick 

 evaporation, we find silica deposited ; round the edge we find a ring 

 of silica thus laid on, and not until the evaporation is continued for 

 a considerable time, do we find the slightest turbidity in the central 

 portions of the water. This experiment is the microscopic repre- 

 sentant, if the term be permitted, of nature's operations in Iceland. 

 Imagine the case of a simple thermal spring whose waters trickle 

 over its side down a gentle incline ; the water thus exposed evapo- 

 rates speedily, and silica is deposited. This deposit gradually 

 elevates the side over which the water passes until finally the latter 

 has to choose another course ; the same takes place here, the ground 

 becomes elevated by the deposit as before, and the spring has to 

 go forward — thus it is compelled to travel round and round, dis- 

 charging its silica and deepening the shaft in which it dwells, until 

 finally, in the course of centuries, the simple spring has produced 

 that wonderful apparatus which has so long puzzled and astonished 

 both the traveller and the philosopher. 



Before an eruption, the water fills both the tube and basin, 

 detonations are heard at intervals, and after the detonation a violent 

 ebullition in the basin is observed ; the column of water in the pipe 

 appears to be lifted up, thus forming a conical eminence in the 

 centre of the basin and causing the water to flow over its rim. The 

 detonations are evidently due to the production of steam in the 

 subterranean depths, which rising into the cooler water of the tube, 

 becomes condensed and produces explosions similar to those pro- 

 duced on a small scale when a flask of water is heated to boiling. 

 Between the interval of two eruptions, the temperature of the water 

 in the tube towards the centre and bottom gradually increases. 

 Bunsen succeeded in determining its temperature a few minutes 

 before a great eruption took place ; and these observations furnished 

 to his clear intellect the key of the entire enigma. A little below 



