Abstract: At least part of a reflector surface covering a rod-shaped light source is a continuous body having such a shape that in a plane perpendicular to the central axis of the rod-shaped light source, a ray emitted from a light emitting point on the surface of the rod-shaped light source in the tangential direction going away from a light conducting plate is reflected back to the vicinity of the light emitting point. According to another aspect, at least part of a reflector surface covering a rod-shaped light source located between the rod-shaped light source and the light conducting plate is part of a parabola whose focus is substantially located on the side face of the light conducting plate in a plane perpendicular to the central axis of the rod-shaped light source.

Abstract: An electromagnetic conductivity meter comprises a core; a primary coil wound around the core; an alternating power source for applying an alternating voltage having a given frequency to the primary coil to excite the core; a tube wound around the core through which a liquid to be measured flows; induction current detecting means disposed at the opposite ends of tube; and an operational means for determining the conductivity of the liquid to be measured from a value of the induction current detected by the induction current detection means.