1853.] OF THE ROYAL INSTITUTION. 333 
Sulphide of Sodium. ; - 0.0088 
Carvonic Acid . > 5 - 0.0557 
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 analyzed 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 eye- 
witness 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 
shew that it has been deposited by the Geiser. But in building the 
mound, the spring must also have formed the tube which per- 
forates the mound; and thus we learn that the Geiser is the archi- 
tect 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, 
