72 OUTLINES OF NATURAL PHILOSOPHY. 



nary lever, and the weight sustained by the fulcrum 

 will be to either of the other two forces, as the dia- 

 gonal of the parallelogram to the side which cor- 

 responds to that force : also the two extreme forces 

 will be to one another inversely as the sines of the 

 angles which their directions make with the above 

 diagonal. 



130. If we would allow for the weight of the le- 

 ver itself, we must suppose its weight to be united 

 in its centre of gravity, and to act there as a third 

 force, added to the power or the resistance, accord- 

 ing to the side of the fulcrum on which it is pla- 

 ced. 



131. When a beam carrying a weight, is sup- 

 ported in a horizontal position by two props, the 

 weights which the props sustain are inversely pro- 

 portional to their distances from the centre of gra- 

 vity of the weight. 



132. If a weight W, be sustained on a horizon- 

 tal plane by three props, (not in a straight line), 

 the pressure on each will be the same as if a single 

 weight were laid on it, so that the sum of all the 

 three weights were equal to W, and their common 

 centre of gravity the same with the centre of gravi- 

 ty of that body. 



a. If 



