Abstract: An indicating apparatus for preventing vehicles from colliding with each other as they pass an intersection of roads includes a vehicle sensing device placed on one of the roads a predetermined distance from the intersection for sensing a vehicle approaching the intersection, an alarm indicating device placed at the predetermined point on the other road, and a control device for causing the alarm indicating device to indicate alarm when the vehicle sensing device detects a vehicle approaching the intersection.

Abstract: A landslide detecting apparatus which is laid under the ground include: a light source; a lens device for converting a beam of light from the light source into a parallel pencil of rays; a condensing lens device; a light detecting device; and a shading mechanism adapted to partly or entirely intercept the pencil of rays in response to external pressures applied thereto. Any change in the earth's crust in a direction to cause a landslide causes the shading mechanism to operate in correspondence with the magnitude of the change so as to partly intercept the parallel pencil of rays and cause a change in the quantity of light detected, making it possible to obtain a quantitative knowledge of the change in the earth's crust.