260 82 



phurous springs and alkaline springs containing free oxygen are found at each of 

 these places. 



The measurements of the emanation in the spring gases apparently contribute 

 very little to an elucidation of the nature of the hot springs. The comparatively 

 large variations in the emanations indicate that the emanation is affected by several 

 factors which have little importance in connection with other properties of the 

 springs. In this regard it is certainly very important to note that the emanation 

 is distinguished from the other gases evolved by the springs, on account of its 

 gradual decay. In two spring gases, originally of the same composition and un- 

 dergoing similar treatment on their way to the earth's surface, there will be less 

 emanation in that which has been longer on the way, owing to the decay of the 

 emanation. This latter factor will therefore doubtless contribute to increase the 

 difference between the amounts of emanation contained in the gases. 



The emanation in springs situated on the same fissure in the earth's crust 

 often increases the nearer one comes to one end of the fissure. This is the case 

 with the three hot springs at Reykir, (Reykir Nos. 1, 2 and 3), the springs at Gra- 

 farbakki and those at Hengill. At the first-named place the springs with the 

 greatest emanation are situated at the south end of the fissure, and in the two 

 other places at the north-east and north ends respectively. The decay of the 

 emanation will possibly account for tiiis, as the spring gases take less time to reach 

 the surface at the end of the fissure where the emanation is greater. This may 

 either be because the subterranean seat of the spring is nearer this end of the 

 fissure, or because the gases, for some unknown reasons, pass more rapidly through 

 the subterranean channels. The great variation in the amount of emanation from 

 the alkaline springs at Hveravellir is probably to a great extent due to similar 

 causes, in that the spring gases often stand for a considerable time in the subter- 

 ranean cavities which, according to the geyser theory I have advanced, are to be 

 found in this locality. The fact that the whole of the emanation does not come 

 from the subterranean seat of the spring would have considerable bearing on the 

 variations in the amounts of emanation. A considerable part of the emanation from 

 the springs is often due to radium contained in the superficial strata. The atmos- 

 pheric water, sinking through the ground, receives a great deal of the emanation 

 produced in these strata, and conveys it to the spring channel. A comparison ,ot 

 the radio activity of the alkaline and acetous springs at Reykjafoss and at Hvera- 

 vellir seems to confirm this. The acetous springs at these places are in my opinion 

 more closely connected with the real subterranean seat of these spring groups than 

 the alkaline springs, which contain gases of atmospheric origin and consequently 

 also atmospheric water in considerable quantities. But the alkaline springs are 

 nevertheless often more radio active than the acetous springs, which is certainly 

 to be regarded as a proof that atmospheric water and air supply the springs with 

 radium emanation from the strata the water has passed through. It is possible 

 that this could be demonstrated experimentally, for there is good reason to suppose 



