Abstract: A noise converter according to this invention is provided with gas conducting spiral passages defined between spirally twisted outer and inner tubes polygonal in cross-section. A gaseous body generating noise flows through the gas conducting passages from one end to the other. Since noise is generated by masses of particles of gaseous body having energy, particles of less energy move forward along a course near the center of each spiral passage whereas those of more energy along the other course near the outside of the passage due to centrifugal force, thereby dispersion and attenuation of energy being performed.

Abstract: A clear view screen (11) comprises a fixed frame (5), a rotating frame (7) and an induction motor (22). The fixed frame (5) has an inner peripheral surface (6) with a V-shaped section, where slits (33) are provided. The rotating frame (7) has an outer peripheral surface (8), which is also V-shaped in section. Compressed air blows into the slits (33) through an air path (35) and an air supply pipe (17), so that the rotating frame (7) is supported rotatably within the fixed frame (5). In this state, the rotating frame (7) is rotated by means of the induction motor (22). As a result, waterdrops and the like adhering to a transparent plate (9) provided in the rotating frame (7) can be removed by centrifugal force.