X = −dV/dx, Y = −dV/dy, Z = −dV/dz;

(1)

and putting

dw− dv= 2ξ, du− dw= 2η, dv− du= 2ζ,
dy dzdz dxdx dy

(2)

dξ+ dη+ dζ= 0,
dx dydz

(3)

the equations of motion may be written

du− 2vζ + 2wη + dH= 0,
dt dx

(4)