The paper describes the results obtained from making visual observations of the paths followed by the several portions of the air-stream. One of the passages being considered was half-sectioned in a plane about which the passage was symmetrical; that is, a plane containing the axes of the several parts of the passage. A flat glass plate was then cemented on to complete the half-passage. With the outlet end of such a passage connected to an engine intake, any sort of flow encountered in engine practice can be reproduced. By introducing gasoline with the entering air, a tracery of fine sharply defined lines on the glass is produced and this was photographed, as is described in detail. Varied shapes of passages were studied in this manner. These are illustrated and the variations in the results under differing conditions are discussed.