A characterization of orthogonal vector fields over ${\bf W^*}$-algebras of type ${\bf I_2}$

In the paper we give a characterization of a $w^*$-continuous orthogonal vector field $F$ over an $W^*$-algebra $\mathcal{N}$ of type $I_2$ in terms of reductions $F$ on the center of $\mathcal{N}$. As an application it is obtained a proof of the assertion that an arbitrary $w^*$-continuous orthogonal vector field over a $W^*$-algebra of type $I_2$ is stationary.