364 Prof. Bischoff oti the Temperature of' 



particles from the rocks over which they pass. But it is hardly 

 to be expected that they would dissolve any other substances 

 than carbonate of lime, if the rocks contain that substance ; for 

 we cannot suspect the presence cf any more soluble salts in the 

 rocks, because if they had ever existed, they would have been 

 washed away already long since. The quantity of carbonate of 

 lime which they dissolve, must also be very inconsiderable, as 

 they have no opportunity of absorbing carbonic acid, while the 

 atmospheric waters which supply the springs are already partly 

 impregnated with this acid, and are also supplied with it from 

 the superficial soil through which they pass. The same train 

 of reasoning is of course also applicable to the water melted 

 from the under surface, whether at the expense of the internal 

 heat of the earth, or by the heat of springs and streams of 

 water ; but with this difference, that in this water we may sus- 

 pect the total absence of carbonic acid, and consequently the 

 least possible power of dissolving the lime. So that the more 

 melted ice is mixed with the streams and springs under the gla- 

 cier, the more will their original contents of fixed substances, 

 and especially of very soluble salts, be diminished ; and thus we 

 may expect to find the smallest proportion of fixed substances 

 in the streams which issue from under the glaciers, in summer, 

 and the greatest proportion in the season when the melting of 

 the glaciers almost or entirely ceases. From this we see that, 

 by analyzing the water of the glacier-streams at various seasons, 

 we may gain results, from which the quantity of ice molted 

 away from the glacier may be inferred. If, for example, an 

 analysis were made at the time when the temperature of the at- 

 mosphere is brought down just below 32°, the water could not 

 possibly be mixed with any but that melted from the under 

 surface of the glacier. If at the same time several neighbour- 

 ing springs were also analyzed, and if the weakest among them 

 still contained a greater proportion of fixed parts than was found 

 in the glacier-stream, it might be concluded, with great pro- 

 babilit)', that the glacier still continued to be melted away on its 

 under surface. In those glacier streams which flow throughout 

 the winter, as, for example, that which issues from the upper 

 Grinclelwnld glacier, the analyses might be continued in the 

 severest frosty weather, and if it should be found always to con- 



