| 摘要 |
A concave mirror, cooperating with a convex mirror on its focus line, is hingedly mounted on one side of a slot in the top wall of a heat-insulated space. The concave mirror has the shape of a surface described by a straight line which moves parallel with said slot on a directrix which forms at the most half of a parabola. The hinge axis of said mirror passes by the parabola vertex. A second concave mirror is hingedly mounted on the other side of the slot and cooperates with a horizontal plane mirror and a small pivotable mirror. |
