The Central Government may, by [notification] [For such notification; see Gazette of India, 13-11-1965, Pt. II, S.3(i), p. 3680] in the Official Gazette, direct that all or any of the powers or duties which may be exercised or discharged by it under this Act shall, in such circumstances and under such conditions, if any, as may be specified in the notification, be exercised or discharged also by any person specified in this behalf in the notification; and any such person may, with the previous approval of the Central Government, by order in writing direct that any power or duty which has been directed to be exercised or discharged by him shall, in such circumstances and under such conditions, if any, as may be specified in the direction, be exercised or discharged by any such person subordinate to him as may be specified therein.