244 Professor Forbes on the Leading Phenomena of Glaciers, 



representing Alpine valleys. In order to trace the motions 

 better, I composed the streams of alternate doses of white and 

 blue fluid, poured in successively. I have had a great number 

 of such experiments made. The results have been preserved, 

 and sections made of them, which I exhibited to the Royal 

 Society of Edinburgh in March 1843, and described in their 

 Proceedings. It may safely be stated, that the results of arti- 

 ficial sections of many of these experimental models, were not 

 to be distinguished from the glacier sections transmitted by 

 me from Geneva six months before, as the results of my ob- 

 servations, which are reprinted from the original woodcuts in 

 pages 237, 240, and 241. I subjoin a figure of one of the 

 experimental models of a viscid fluid, which has been sepa- 



Vicw of a model shewing the curves generated (experimentally) by the motion of a viscous 



fluid. 



arrangement of the powder on the surface of the plaster model, and the lamellar 

 arrangement of the ice in the interior of the glacier. 



The least distance which can ever exist between a side and a central particle of 

 a canal-shaped glacier, is half the breadth of the glacier. But the unequal motion 

 of the centre and sides tends continually to separate them wider apart, and to 

 distend the row of particles which connects them. The sti'uctural bands are, 

 therefore, perpendicular to the line of greatest tension, and hence crevasses will 

 naturally occur, crossing the structure at right angles, which I have found empiri- 

 cally to be the case. In pursuance of this principle the crevasses in an oval 

 glacier are radiating ones ; those of a canal-shaped glacier must be slightly convex 

 upwards, and this is perfectly confirmed by the crevassed appearance which the 

 models described at the commencement of this note present. They are fissured 

 in a direction exactly perpendicular to the strise of the powdered surface. 



