抄録
As a method for qualitative judgment of a perfect ball, two faces of the ball are observed at the same time. A horizontal mirror is used in practical examination. Twin Arago points that appear at the center portion in the shadow are used for qualitative estimation of sphericity. The clear concentric-circular fringes, which spread in the whole space between the Arago point and the circumference of the ball, are also an effective way to judge the perfect ball qualitatively. The panchromatic light source provided by a white-light laser gives clearer images than monochromatic laser light source. The color decomposition from the white mode into the monochromatic modes enables visual recognition of the wavelength dependence of the diffraction angle.
