nrise. The color, the duration, and the intervals of
flashing indicate the position of the beacon. In revolving lights
the beams, concentrated by powerful lenses, sweep the horizon as
the lantern about the light revolves. Flashing lights are produced
when the light is obscured at given intervals. Fixed lights burn
with a steady flame. In some instances a sector of colored glass is
set so as to cover a given part of a channel. Range lights, set so
that one shows directly above the other, are used as
channel-markers.

[Illustration: CITY OF NEW YORK AND VICINITY, WITH HARBOR
APPROACHES.]

The use of lights may be seen as a vessel enters New York Lower
Bay. A steamship drawing not more than eighteen feet of water may
enter through Swash Channel (_follow the course on the chart_). In
this case the pilot makes for Scotland lightship, and merely keeps
New Dorp and Elmtree beacons in range, giving Dry Romer a wide
berth to starboard, until Chapel Hill and Conover beacons come into
range on his port side. The vessel is then held on a course between
Coney Island and Fort Tompkins lights until Robbins Reef light
shows ahead.

For the liners that draw more than eighteen feet the task is more
difficult, inasmuch as the channel is tortuous. At Sandy Hook
lightship a course lying nearly west takes the vessel to the outer
entrance of Gedney Channel, marked by two buoy-lights. In passing
between the lights the vessel enters the channel, which is also
covered by the red sector of Hook beacon. The pilot continues
between the buoy-lights until Waacaack and Point Comfort beacons
are in range, and steers to this range until South Beacon and Sandy
Hook light are in range astern. The helm is then turned, keeping
these lights in range astern until Chapel Hill and Conover beacons
are in range on the port bow. Turning northward nearly eight
points, the pilot holds the bow of the vessel between Fort Tompkins
and Coney Island lights, keeping sharply to his range astern, until
Robbins Reef light comes into view through the narrows. From this
point on, the shore lights are the pilot's chief guide.

So difficult are harbor entrances, that in most cases the
underwriters will not insure a vessel unless the latter is taken
from the outer harbor to the dock by a licens