(a) Whoever willfully or negligently obtains or fails to return to a public library located within the City any book, magazine, pamphlet, manuscript, picture, clipping or other property belonging to and borrowed from such public library, within thirty days from the date of the posting by registered mail of a notice addressed to such person at the last address furnished the public library, and which notice may be given at any time after the date on which such person should have returned the loaned property, in accordance with the rules of the public library, shall be presumed to have converted the same to his use.
(b) Whoever violates this section is guilty of a minor misdemeanor. No penalty shall be imposed in any case where restitution in value is made prior to the expiration of the thirty day period, nor in any case where the return of such book, magazine, pamphlet, manuscript, picture, clipping or other property is rendered impossible by causes beyond the control of the borrower.