Dictionary of Ichthyology  

float = 2) a plastic, cork or wood device that enables a baited hook to be suspended in the water column and enables fish biting on the hook to be detected by movement of the float. Usually painted distinctively, e.g. fluorescent colours, particularly at the tip. Floats are attached to the fishing line through small holes at the bottom of the float or by means of silicone tubes slipped over the float with the line trapped between the tube and float. Split shot or some other weight is attached to the line below the float so that the line sinks and the float achieves a suitable level above the water and is sensitive to bites. Bites may be evidenced by the float zooming underwater, by wiggling movements, by a slight rise as a fish picks up bait off the bottom, and other subtle movements. Strikes can be made immediately the float moves or delayed to give the fish time to take in the bait - this varies with bait type, species of fish and sophistication of the individual fish. Immense number of types and materials used, some with carbon fibre stems and tips or heavy and stable lignum stems. Also called bobber in North America or waggler in Britain..
A Book on Angling, by Francis Francis, 1876 from Wikimedia Commons: http://commons.wikimedia.org/wiki/File:Plate_II-Francis-The_Slider.JPG

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