In treating the equations of rotation of a solid body about a fixed point, it is usual to employ the principal axes of the body as the moving system of coordinates. Cases, however, occur in which it is advisable to employ other systems; and the object of the present paper is to develope the fundamental formulæ of transformation and integration for any system. Adopting the usual notation in all respects, excepting a change of sign in the quantities F, G, H, which will facilitate transformations hereafter to be made, let A = Σ
m
(
y
2
+
z
2
), B = Σ
m
(
z
2
+
x
2
), C= Σ
m
(
x
2
+
y
2
), -F = Σ
myz
, -G = Σ
mzx
, -H = Σ
mxy
;