| 摘要 |
PURPOSE:To improve the stability and reproducibility by making the top surface of a float which faces the wall surface of a pressure receiving pipe containing liquid and has symmetrical planes into a specular surface. CONSTITUTION:A float 1 has the symmetrical plane or concave curved surfaces opposite the tube wall 4. The float 1 is made of a material which has small specific gravity and is not wetted with working liquid 6 or working liquid 6 which does not wet the material is used. Here, surface tension operates uniformly on the float 1 and a reflector 3 at the center part is held at the center position of a U-shaped tube and does not shift from the optical axis. Further, the float 1 floats on the liquid surface, so fluctuations of the liquid level due to the vibration of a floor surface are suppressed and smoothed. Consequently, reflected light which has the stable optical axis is obtained from the reflector 3 on the float 1. |
