The sightings of July 26–27 also made front-page headlines, and even led President Harry Truman to personally call Capt. Ruppelt and ask for an explanation of the sightings. Ruppelt, remembering the conversation he had with Capt. James, told the President that the sightings might have been caused by temperature inversion, in which a layer of warm, moist air covers a layer of cool, dry air closer to the ground. This condition can cause radar signals to bend and give false returns.