Additional Manuscripts a

WW must have missed a footnote which answers the observations he made regarding the two sheets he sent him on glacial theory [see JDF to WW, 16 June 1843]: the structural shells 'arise at any point of the glacier from the tendency to separation of the surfaces, determined by the line of least resistance'. JDF describes an experiment (with pictures) he has constructed to show the movement of the glacier: 'I think that your difficulty about the motion of any particle of the ice being urged upwards over its neighbours in front, will appear to you to vanish when you recollect that the whole resistance to the motion of a particle is compounded of the resistance in front from the stiffness or viscosity of the particles in advance and the weight of the particles above'.