The text describes that in the dioptric method, all the rays emitted by one large flame are intercepted by glass lenses or prisms at a short distance from the flame, and are bent or refracted, so that they issue from the lighthouse lantern in a compact beam[1]. In this method, a single lamp is used for dioptric lights and is placed in the middle of the lantern[1]. The light from the flame is intended to be sent out onto the sea all around a tower standing on a rock some miles from the shore[1]. The author likens the effect to a huge umbrella of light, with the tower as the stick[1]. The light is enclosed in what may be described as a glass hive[1]. The property of each prism is such that a ray falling upon one of its sides is refracted through the substance of the glass at an angle onto another side, from whence it is totally reflected out through the third side in an unaltered direction from that in which it entered the prism[1].
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