16 Mr. WHEWELL on the 
The only forces which act upon the points, are the ¢ensions, or 
reactions of the six rods Om, Om’, Om’, mm’, mm", m'm’. And if 
these be resolved at each point m, m’, m’, into three rectangular 
components X, Y, 2, X’, Y’, 3’, X”", Y”, 3", we shall have 
eX, Oa Vy eee 
de em? ade m ” e m 
es, xX! Cy Ss gee gee ac): 
dt m? dt’ m? dt 
ad’ a!’ ty = dy" te y"’ diz! gi 
dt md?) wun 2 at m’ 
Now let the force which acts on m, and which is composed of 
X, Y, &, be resolved parallel to Om, Om’, Om". And since x is 
the cosine of the angle which Om makes with X, we shall have 
Xx for the part of the force arising from X, acting on m in the 
direction Om. Similarly, Yy and <2, are the parts arising from 
Y and &. 
Hence, the whole force on m, 
in direction Om is Xx + Yy + &z, 
vues. OM IS Ad -+-.Yo" 4 32’, 
Sreeae Om" is Xx" + Vy" + 82". 
Similarly, the force on m’ 
in direction Om is X'x + Y'y + &z, 
Riker waicere:s Om! is X’e + Vy + &2', 
isiaysncts « Om! aS Mae oe May” ees 
And the force on m“ 
in direction Om is X"x + YV'y + 8"z, 
A Crete 2... Om!’ is X"a! + Y"%y' + "2, 
ec pederee Om is Xs" + Wig as, 
