I am a light, set up to guide and warn mariners, from certain dangers. I exhibit two

I am a light, set up to guide and warn mariners, from certain dangers. I exhibit two lights, which show red and white, and thus indicate two different channels, which mark out the way to be followed, in order to avoid certain beacons, which are erected to warn from other dangers. I am placed here, as a mark buoy, to show where the channel is, and must be carefully distinguished from other buoys, which are placed, to mark where the