Malfroy. — On Geyser-action at Eotorua. 687 



hot and cold water within the geyser-tube will thus produce 

 every phenomenon of geyser-action to be observed at Eotorua ; 

 and I am led to believe that, by studying the action of geysers 

 and springs in this district, they could in most cases and to a 

 certain extent be regulated and controlled. 



Geyser-action may be briefly explained according to the 

 foregoing, as follows : Supposing that an even-sized tube full 

 of water becomes so hot that steam generated at the bottom, 

 under heavy pressure, rises through it without being con- 

 densed, there comes a time when several globules of this steam 

 will be in the tube at the same time, and as they rise to the 

 surface they will expand in proportion to the release of 

 the pressure exerted upon them, and when coming near the 

 surface they, as it were, explode, throwing the small quantity 

 of water contained in the tube into the air, forming irregular 

 intermittent explosions. Eruptions of longer duration can be 

 explained thus : The actual weight of water in the tube, acting 

 as a valve on the force, may by means of these globule explo- 

 sions find itself suddenly released by, say, half the pressure of 

 the column of water. The equilibrium being thus destroyed, 

 the pent-up steam rushes up the geyser-tube with a force 

 proportionate to the depths at which the reservoir containing 

 this force may be situated, aiad, acting on the principle of a 

 Giffard ejector, the peiit-up steam rushes up the tube, taking 

 up with it a certain quantity of the water which may find its 

 w^ay into the tube, and ejecting it in the air, in the form of 

 high, low, or intermittent geysers, in proportion to the different 

 size, position, force, and volume of the spring, and other cir- 

 cumstances of the case. 



I have also observed that the chemical composition of the 

 water is sensibly altered by the different actions of the geysers ; 

 thus, if the geyser is made to ]olay very actively, the water 

 becomes softer to the touch, it being more silicious and oily 

 than when the geyser-action is subdued and allowed to boil 

 up quietly. This will account for the comparative rapidity 

 observed in the formation of terraces or mounds around the 

 most active geysers, and the very small amount of silica 

 deposited by springs of less pressure and activity. 



Postscript. 



Doubts having been expressed, by some gentlemen who 

 have studied and written on the thermal action of this district, 

 as to the theory propounded in the foregoing paper, I have 

 constructed an apparatus (see PI. XLII.), with which I can 

 illustrate the hot spring, the constant, short- or long-interval 

 intermittent geyser, the steaming fumarole, and the mud- 

 volcano — in fact, all the different series of phenomena to be 



