CLOUDS AND RIVERS, ICE AND GLACIERS. 71 



we able to pusli our measurements quite across the 

 glacier. Why ? In attempting to do one thing we are 

 often taught another, and thus in science, if we are only 

 steadfast in our work, our very defeats are converted 

 into means of instruction. We at first planted our 

 theodolite on the lateral moraine of the Mer de Glace, 

 expecting to be able to command the glacier from side 

 to side. But we are now undeceived; the centre of 

 the glacier proves to be higher than its sides, and from 

 our last two positions the view of the ice near the oppo- 

 site side of the glacier was intercepted by the eleva- 

 tion at the centre. The mountain slopes, in fact, are 

 warm in summer, and they melt the ice nearest to them, 

 thus causing a fall from the centre to the sides. 



171. But yonder on the heights at the other side of 

 the glacier we see a likely place for our theodolite. 

 We cross the glacier and plant our instrument in a 

 position from which we sweep the glacier from side to 

 side. Our first line was below the Montanvert, our 

 second line above it ; this third line is exactly opposite 

 the Montanvert ; in fact, the mark on which we have 

 fixed the fibre-cross of the theodolite is a corner of one 

 of the windows of the little inn. Along this line we 

 fix twelve stakes on July 20. On the 21st one of them 

 had fallen; but the velocities of the remaining eleven 

 *.n 2 I hours were found to be as follows : — 



