NEW ORLEANS  One of the world’s richest men toured one of America’s poorest cities on Tuesday, a whistle-stop visitor from a distant land come to see his good works in a place still needing a stranger’s kindness.

After Hurricane Katrina, the emir of Qatar donated $100 million to the Gulf region, intended to help rebuild housing, hospitals and schools. But the effect of his visit to New Orleans on Tuesday seemed muted, as two universes peered at each other through the dark smoked glass of his motorcade.

It was through that filter that the genial, burly emir, Sheik Hamad bin Khalifa al-Thani, saw the unhealed landscape of the Lower Ninth Ward, touring the scarred lots in a police-guided caravan of luxury vans and cars as the few people out in the spring sunshine stared blankly back at the opaque windows. Open-mouthed astonishment registered on some of the faces at street level.

The emir did not get out to walk through the ruined neighborhood. The ruler of a tiny country ranked third on a United Nations wealth list, he had given generously, and Tuesday he sped on, later telling students at Xavier University that “we are all neighbors in a small and fragile world” but deciding in this instance against crossing a bridge too far.