1836.] On the Position of Frames in a Sloping Gallery. 371 



To the Editor of the Madras Journal of Literature and Science. 

 Sir, 



At page 335 of vol. 2, a solution of the problem of the proper posi- 

 tion of a prop upon an inclined plane is given, but, it is to be remarked, 

 the axiom on which the first solution is attempted, does not apply to the 

 subject in question ; in all cases of equilibrium where the two forces do 

 not act in the same line, there being a third force to be accounted for, 

 which is there neglected, nor is the reasoning in application of the 

 principle correct, vide diagram, page 336, vol. 2. If the direction of 

 the power is taken in the line D C, the line B A must also be made per- 

 pendicular to it, which is not done. The propriety of placing a prop 

 perpendicular to the direction of the mine, can, I think, hardly be 

 denied, when the sub- 

 ject is properly consi- 

 dered. Suppose A B to 

 represent a mass of 

 stone, to be supported 

 in an inclined position, 

 would not the prop na- 

 turally be placed in the 

 direction D C, and while 

 the stone was support- 

 ed by a firm support at 

 B, would not the prop 

 be placed in the same 

 position, even if the 

 ground was sloping ? 

 Here the force of gra- 

 vity is acting in the di- 

 rection C E, but be- 

 comes resolved into two 

 other forces, C B and C 

 D, to oppose which, the 

 prop is placed in the 

 direction of its action, 

 which, it is hardly ne- 

 cessary to prove here, 

 would be its best posi- 



