THE FORMS OF WATER 



Grancle Jorasso. 



Col da 

 Geant. 



Chapeau. 



FlG. 6. OUTLINE-Pl^AN, SHOWING THE MEASURED LINES OB 1 THE Ml!U I)!! GLACE AND ITS TmBlTTARIBa. 



of the Arvoiron, and talking about going 

 into it, its roof gives way and falls with the 

 sound of thunder. It is not. therefore, with- 

 out reason that I warned you against enter- 

 log these vaults in summer. 



163. We ascend to the Montanvert Inn, 

 fix on it as a residence, and then descend to 

 the lateral moraine of the glacier a little be- 

 low the inn. Here we erect our theodolite, 

 and mark its exact position by a plummet. 

 We must first make sure that our line is per- 

 pendicular, or nearly so, to the axis or mid' 

 die line of the glacier. Our instructed assist- 

 ant lays down a long staff in the direction 

 of the axis, assuring himself, by looking up 

 and down, that it is the true direction. 

 With another staff in his hand, pointed 



toward our theodolite, he shifts his position 

 until the second staff is perpendicular to the 

 first. Here he gives us a signal. We direct 

 our telescope upon him, and then gradually- 

 raising its end in a vertical plane we find, 

 and note by sketching, a standard point at the 

 other side of the glacier. This point known, 

 and our plummet mark known, we can on 

 any future day find our line. (To render the 

 measurements more intelligible, 1 append an 

 outline diagram of the Mer do Glace, and of 

 its tributaries.) 



164. Along the line just described ten 

 stakes were set on July I'.th, 1857. Their dis- 

 placements were measured on the following 

 day. Two of them had fallen, but here are 

 the distances passed over by the eight re- 



