248 70 



These gases have also some interest in other respects. 



In the following table I have collected the analyses within my knowledge of 

 spring gases from Namafjall. 



It appears from this table that a slight change in the composition of the gas 

 took place between 1845 and 1871, the amount of hydrogen becoming a little 

 greater. This change seems to have developed along the same lines with surprising 

 rapidity during the years 1871 and 1906. My gas samples from Namafjall show 

 the greatest amount of hydrogen that has been found in gases evolved by the hot 

 springs of Iceland. As already emphasized, one must exercise great care in drawing 

 conclusions from changes in the composition of the spring gases, but as the mud 

 pools at Namafjall are grouped together within three well-defined areas, one of 

 which it is not possible to approach, and the spring gases in each of these three 

 groups of springs have in all essentials the same composition, we shall not be far 

 wrong in assuming that the alterations in the composition of the spring gases, 

 shown in the above table, correspond fairly well to the actual conditions. 



Of course the few results given cannot help us to determine whether the 

 alterations have taken place suddenly or as the result of a gradual process. 



Assuming that Bunsen's theory regarding the process of the formation of 

 hydrogen and sulphuretted hydrogen in the springs is correct, Christensen ' ex- 

 presses his opinion that the increase of hydrogen must be regarded as a sign that 

 the spring gases have been highly heated. If this be so, we must suppose that 

 the terrestrial heat at Namafjall is on the increase. However, comparing my ob- 

 servations of the terrestrial heat at Namafjall with previous descriptions of the 

 locality, I have been unable to find the least sign of such an increase in the 

 thermal activity on the earth's surface. - 



With regard to their composition, the spring gases from Kerlingarfjöll and 

 Hengill most closely resemble the gases evolved by the hot springs at Myvatn, 

 especially on account of the large quantities of hydrogen. The analyses of the 

 gases from the hot springs at Kerlingarfjöll and Hengill harmonize very closely 



' loc. cit. p. 242. 



- I have since learnt that tlie hihabitants of the district at Myvatn are of tlie opinion that tlie 

 tliermal activity really is increasing. 



