Section 4 Exemptions from registration under s. 3.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F1

The F2Secretary of Statemay by order grant . . . F3exemptions from registration under the last preceding section, by reference to such classes of persons, and such descriptions of mobile radioactive apparatus, as may be specified in the order.

Any exemption granted by an order under the last preceding subsection may be granted subject to such limitations or conditions as may be specified in the order.