1845.] VISCOUS THEORY OF GLACIER MOTION ILLUSTRATED. 77 



stated (under Head III. above) that the velocity of any glacier 

 is proportional to the completeness of its saturation with water 

 at the time. The bas-nev6s, or old avalanches, furnish very 

 little water at their lower extremities. 



I have now gone through these observations, made by persons, 

 it may be assumed, not particularly desirous to find results con- 

 firming a theory which they have opposed, but which it may be 

 hoped they will oppose no longer, when their own results speak 

 in language so unequivocal. My analysis has been succinct, 

 but complete and impartial. The facts are stated as given, 

 without selection or suppression. 



XL ILLUSTRATIONS OF THE VISCOUS THEORY OF 

 GLACIER MOTION. PART I. CONTAINING EXPERI- 

 MENTS ON THE FLOW OF PLASTIC BODIES, AND OBSERVA- 

 TIONS ON THE PHENOMENA OF LAVA STREAMS.* 



1. Plastic Models. 2. Analogy of Glaciers to Lava 

 Streams. Note on the Velocity of Lava. 



1. PLASTIC MODELS. 



In the concluding chapter of my " Travels in the Alps of 

 Savoy," I have shown how the obscure relations of the parts of 

 a semifluid or viscous mass in motion (such as I have attempted 

 to prove that the glaciers may be compared to) may be illus- 

 trated by experiment. 



The larger models, there described and figured, showed 

 very clearly the precise effects of friction upon the motion of 

 such a mass. They were formed of plaster of Paris, mixed 

 with glue, and run in irregular channels, and the relative velo- 



* From the Philosophical Transactions for 1846, p. 143. Received by the Royal 

 Society of London March 15 Read April 10, 1845. 



