270
HARBOUR ENGINEERING.
With the object of still further strengthening the serviceable illumination,
mirrors were placed above and below the lenses so as to reflect many of the
Figs. 239. —Single Flashing Light. Figs. 240. —Single Flashing Light. Figs. 241.—Single Flashing Light.
I panel of 157° ; Dioptrie mirror 170°. 2 panels of 167°. 4 panels of 90°.
rays which escaped the latter. This conjunction of the reflective and re-
fractive principles led to the adoption of the term catadioptric to distinguish
it. The mirrors were eventually replaced by lenticular prisms capable of