A mother appeals from an order of the DeKalb Superior Court modifying the visitation rights which had been previously granted to her husband, the appellee herein, in an agreement incorporated into their final decree of divorce. The trial judge changed the visitation rights of the husband from "reasonable visitation privileges" to specified visitation periods. We affirm.

Appellant contended throughout the proceedings below and now appeals on the ground that a change of circumstances and conditions substantially affecting the welfare of the children had not been shown. In reviewing the correctness of rulings in child custody cases, we do not substitute our judgment on the evidence for that of the trial judge. It is our duty to affirm unless there is an abuse of discretion in the trial court, and we find none here. See Fowler v. Fowler, 231 Ga. 572 (203 SE2d 235) (1974), and Haberman v. Bivens, 235 Ga. 537 (1) (221 SE2d 11) (1975).