CHANNEL DEMARCATION.
269
central lens with annular adjuncts, the result being a concentration of the
rays in a corresponding series of pencils, with intervening sectors of darkness.
Such an arrangement lends itself to the production of flash-lights by the
Figs. 238. —Fixed and Flashing Light.
4 fiashing panels of 45° each ; 4
fixed panels of 45° each.
Figs. 237. —Fixed Light of 180° and
Dioptric Mirror of 180°.
Figs. 236. —Fixed Light of 360°.
revolution of the lenticular apparatus around the light, the illuminations
being alternated with brief periods of obscurity, either total or partial,
according as the apparatlis is holophotal throughout, or combined with a
fixed light.