The private pilot did not visually check the fuel level prior to departure, but his fuel guages indicated the left tank was 3/4-full and the right fuel tank was 1/4-full. He departed with the fuel selector on the left tank and flew for an hour before he picked up a friend and continued with the flight. The pilot and his passenger flew to another airport and landed. They then taxied back to the runway and departed. On takeoff, the pilot made a left hand turn and the engine began to sputter and then stopped producing power. The pilot was unable to return to the airport, so he made a forced landing to a field. Examination of the airplane by a Federal Aviation Administration inspector revealed the left fuel tank was empty and the right tank had some residual fuel inside.