63 241 



the boiling pointât that elevation, it is more probably due to the substances dissolved 

 in the spring water and too strong a heat supply from heated steam, than to the 

 tendencj' of the spring water to become superheated. 



That the channels be crooked, can no longer be regarded as a necessary 

 condition of the intermittance or periodicity of the springs, for the latter, as 

 already mentioned, could easily be in a constant stale of ebullition, even though 

 their channels are crooked. On the other hand the irregularity of Hie channels 

 may in several different ways influence the progress and character of the eruptions 

 of the periodic springs; they tend especially to shorten the eruption, as the water 

 is collected in the bends, and forms stoppages to the steam current through the 

 channel. 



It is evident that special circumstances in the individual springs may greatly 

 influence the character and period of the eruptions. In most of the springs there 

 is a cup-shaped hollow at the place where the spring channel reaches the surface. 

 Owing to the rapid loss of heat at the surface, the spring water gathering in this 

 hollow is kept considerably cooler than the water deeper down in the channel. 

 The rapidity of the loss of heat at the surface is evidenced by the temperature 

 measurements made by Bunsen and Descloizeaux at "Störi Geysir" and Strokkur. 

 This is also borne out by our measurements of the temperature of the water at 

 the surface and at the bottom of Basaliver and Vai^malahver at Grafarbakki. 



During the eruption, the steam current from the orifices in the bottom of the 

 basin is generally so strong that the channel below is kept free from the cold sur- 

 face water in the basin, but if the steam current is stopped for a moment, or 

 weakened to any extent, the surface water runs down into the channel. 



In many cases this will result in the entire cessation of the eruption, because 

 the pressure produced by the water is increased, at the same time as the tension 

 of the vapour is decreased on account of the temperature in the channel being 

 lowered by the cold water. 



At Grafarbakki and, generally speaking, in most of the spring groups that 

 contain periodic geysers, there are constantly boiling springs and periodic geysers 

 side by side. Hence it is evident that two entirely independent channels are often 

 found side by side in the earth. It is therefore quite possible that two or more 

 really independent channels may be united to one channel beneath the surface of 

 the earth. Only one of these channels being capable of causing periodic eruptions, 

 suffices to render the spring itself periodic. 



In the case of several geysers, the eruption takes place in all the channels at 

 once, for as soon as the eruption in one of the channels has relieved the pressure 

 due to the water column in the common channel, the decrease of the pressure will 

 give rise to an eruption in the other channels. With other geysers the decrease 

 of the pressure is not sufficient to cause an eruption in the remaining channels, 

 and as an interesting medium between these two extremities, we have geysers 

 where the eruption in the remaining channels only takes place when the eruption 



