192 APPLIED MECHANICS 
BD and DA respectively. The sense of these forces is also deter- 
mined, and it will be observed that the internal forces in the bars — 
BD and DA both act towards the joint 1, therefore these bars are 
in compression. In drawing the triangle (m) the forces have been 
taken in the order in which they occur in going round the joint 1 
in the watch-hand direction, beginning with the known force AB. 
Beginning with BA, and going round the joint in the opposite direc- 
b b a a 
@) dc d (m) 
<t. 
< 
e 
~-_- 
= 
e 
pel 
an 
o 2. 
: 
a 
> 
> 
> 
Fig. 262. 
tion, the triangle (s), which is similar to (m) but differently situated, 
is obtained. 
Passing next to the joint 2, the three forces acting there are known 
in direction, and the magnitude of one of them, BD, has been determined . 
by the drawing of the triangle (m) or the triangle (s). Beginning with 
DB, and taking the forces in the order in which they occur in going © 
round the joint in the watch-hand direction, the triangle of forces (n) 
is drawn. If the forces be taken in the order in which they occur 
in going round the joint in the opposite direction, beginning with — 
BD, the triangle (wv) is obtained. Proceeding next to the joint 3, 
the triangle (0) is obtained when the forces are taken in the watch- — 
hand order, and the triangle (v) is obtained when the forces are taken in — 
the opposite order. i 
The construction of the three triangles (m), (), and (0), or the three 
triangles (s), (w), and (v), determines the magnitude and sense of each of — 
the three internal forces, and also the magnitudes and sense of the 
external forces BC and CA, 
