A notice of the passage of the resolution required in the last preceding section, embodying a copy of said resolution, shall be served upon the owner of each piece of property to be assessed, said service to be made in the manner provided by this Charter for serving notices herein required; provided, that if it appears by the return, in any case, that the owner cannot be found, then a notice of the passage of said resolution shall be published in some newspaper of general circulation in said City once a week for two consecutive weeks, and such notice, whether by services or publication, shall be completed at least three days before said improvement is begun or the assessment is levied, and the return of the officer serving such notice or a certified copy of said return, or when published, the certificate of the publisher of said newspaper shall be prima facie evidence of the service of the notice as herein required. Notice upon infants may be served on their guardian, and upon insane persons, by their committee.