388 The Laws of Statical Equilibrium. 
right line, at the extremities of which S, T, 
the forces F and G act in the directions SB, 
TB ; also, let ST be sustained at L by a force 
K acting in BD, and a statical equilibrium 
will be produced by Art. 6. Now let the 
lines of direction SB, TB converge to a 
point infinitely distant from ST; then will 
the angle SBT be evanescent; and we have 
seen the angles LSB, LTB, are supplemen- 
tal to each other; asSL: LT::G@:F; which 
is a known property of the straight lever ; 
and if SLV represent a crooked lever, the 
proportion stated above is universal, viz. as 
LSxsine LSB: LVXsine LVB::G: Fl 
Art. 14. Vide fig. 3. Let AB, CB and 
DB be the direction of two forces-F, G, and 
their equivalent K ; from-any point P, not in 
DB, draw PS, PT and PV perpendicular to 
AB, CB and DB respectively ; then Fx SP, 
GxTP and KxVP are called the momenta 
of F, G and K referred to the point or centre 
P. Now no force whatever applied to the 
point P, can keep the material point B in 
equilibrio, when acted upon asin ‘the figure, 
by Art. 4; because the direction of such a 
force will either be parallel to: DB the direc- 
tion of K, or it will form an angle with it; 
therefore if PV be an inflexible line, capable 
of revolving about P, the force acting in the 
