384 The Laws of Statical Equilibrium. 
ABC. For if BD be not in the plane BAC, 
then BACD is a pyramid, and the solid 
angle D is contained by three triangles; of 
which ADC is one; therefore the sides AD, 
CD include anangle; consequently the point 
B cannot remain in BD; but it has been 
shewn to remain in BD. 
Art. 6. Let K denote in magnitude the 
force, with which B isurged by the joint ac- 
tion of F and G in the right line DB; then 
F, G, are called the components, and K their 
equivalent. These things being stated, it will 
appear evident from Art. 4, that if a force 
equal to K be exerted at any point of DB 
produced or not, in opposition to the joint 
effect of F and G, action and reaction will 
take place, without the production of motion, 
which is astatical equilibrium, by Art. 1. It 
is easily proved in like manner, that if F and 
K be two forces acting in the right lines AB, 
DB, and a third force G be opposed to their 
joint effect in the line CB or CB produced, 
statical equilibrium will ensue ; viz. G is the 
equivalent of F and K ; hence any one of the 
three forces F, G and K, is the equivalent, 
and the remaining two are its components. 
Art. 7. It appears from Art. 5, that the 
point B is retained in DB by two equal and 
contrary forces acting at B perpendicular to 
