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Proceedings of Boy al Society of Edinburgh, [jan. 31 , 
the earth mass, thus tacitly neglecting the boundary conditions. 
Rankine, in short, neglects the friction between the earth mass and 
the wall, or supposes the wall to he perfectly smooth. Dr Maurice 
Levy and Professor Boussinesq have worked at the problem thus 
presented, but the author is only partially acquainted with Prof. 
Boussinesq’s results, and not at all with Dr Levy’s. In 1881 
Mr Benjamin Baker read a paper before the Institution of Civil 
Engineers, “ On the Actual Pressure of Earthwork ” — a valuable 
contribution to the literature of the subject, to which reference will 
afterwards be made. An interesting communication from Professor 
Boussinesq is printed with the correspondence appended to the 
paper, which will be found in vol. lxv. of the Proceedings. 
The author will confine himself to the case where the surface of 
the earth to be retained is level. Rankine’s hypothesis of a 
granular material and the fundamental principles before mentioned 
are assumed. 
Fig. 1 . — Vertical Section of a Right Prism of Earth. 
Let ABC be a vertical section of a right prism of earth, whose 
length-axis is parallel to the inner face of the wall, which will 
here be assumed to be vertical. Let BC be in contact with the 
wall, and AC horizontal ; also, let the prism be of unit length, and 
let the transverse dimensions be very small. 
