. "'Every obscene, lewd, or lascivious, and every filthy book, pamphlet, picture, paper, letter, writing, print, or other publication of an indecent character, * * * is hereby declared to be nonmailable matter. * * * Whoever shall knowingly deposit, or cause to be deposited for mailing or delivery, anything declared by this section to be nonmailable, * * * shall be fined not more than five thousand d" . . . . . .