116 Proceedings of the British Association. 



but by the adoption of the new process, a remarkably strong charge 

 was communicated by one single stroke of the balls of the magnet 

 over the bar. 



Dr. Robinson exhibited and described the Orthochronograph, in- 

 vented by the late Mr. Lowman, which, however, the Earl of Rosse, 

 Prof. Stevelly and others, considered less accurate than other known 

 instruments. 



' Account of an attempt to establish the plastic nature of glacier 

 ice by direct experiment,' by Prof. J. D. Forbes. These experiments 

 were made in the month of August last upon the Mer de Glace of 

 Chamouni, with the view of establishing that the increasing velocity 

 of a glacier, from the side towards the centre, takes place (when the 

 declivity is not very great) by the insensible yielding of one portion 

 of the ice past another, without great rents at measurable distances 

 producing discontinuity in the motion. The only permanent marks 

 left by such differential motion are the veins, or blue- bands, to which 

 the author has, in his published writings, attributed such an origin. 

 A transverse line was drawn partly across the glacier in the most 

 compact part which could be found, which was quite devoid of open 

 crevices for a considerable space. The theodolite was planted over 

 a fixed mark in the ice at the extremity of this line nearest to the 

 lateral moraine of the glacier ; and the relative, or differential, velo- 

 city of the parts towards the centre were determined at short inter- 

 vals, and have been projected in a curve. This curve was shown 

 to the meeting. It is evidently a continuous curve, convex towards 

 the valley, and not a zigzag motion, such as must have resulted from 

 distinct rents parallel to the length of the glacier. The length of the 

 line, originally straight, whose deformation was observed, was 90 feet, 

 and the ordinates of the curve were determined by accurate measure- 

 ments at forty-five stations two feet apart. The experiments on the 

 continuous flexion of the transverse line were extended over a longer 

 period, at points 30, 60, 90, 120, and 180 feet from the theodolite, 

 with similar results. The author concludes, \ st, that the sliding of 

 the mass of the glacier over itself by insensible gradations cannot be 

 denied ; and that it is sufficient to account for the observed excess 

 of progress of the centre above the sides of the glacier ; 2nd, that 



