Dublin Police Act, 1842

Constables may apprehend persons offending within their view whose name and residence are not known.

26. It shall be lawful for any constable belonging to the Dublin police, and for all persons whom he shall call to his assistance, to take into custody without a warrant any persons who within view of any such constable shall offend in any manner against this Act, and whose name and residence shall be unknown to such constable, and cannot be ascertained by such constable.