XXIV. On the Theory of the EquiUbrhtm of BocUen in Contact. By the 

 Rev. H. MoSELEY, M.A., of St. John'.s College, Profe.s.mr of 

 Natural Philoso2)hy and Astronomy in King\s College. London. 



[Read May 15, 1837.] 



In a paper on the Theory of the Arch, read before the Cambridge 

 Philosophical Society in October 1833, and publislied in the fifth \^olume 

 of their Transactions, I have discussed the conditions of the equilibrium 

 of a system of bodies in contact, on a principle referring it to the direction 

 in respect to the surfaces of contact of a certain line, given in terms of 

 the magnitudes and directions of the forces which compose the equilibriimn. 

 The condition that no one portion of the system shall turn on the edge 

 of its surface of contact with another, being determined by the condition 

 that the point at which the line leaves the surface of any one of the con- 

 tiguous bodies, to enter the adjacent body, shall be within the boundary 

 of the common surface of contact of the two ; and the condition that 

 no two contiguous bodies shall slip upon one another, by the condition 

 that the direction in which this line intersects their common surface shall 

 lie within a certain angle, which I have called the "limiting angle of 

 resistance," and which is dependent for its magnitude on the circumstances 

 of the friction of the two surfaces upon one another. 



If a surface be imagined to intersect tlie system, and continually to 

 change its position, and, if necessary, its form so as to coincide, in order, 

 with all the surfaces of contact, and if, in each position, the resultant be 

 taken, in respect to those forces which are impressed upon one of the 



