_Various Types of UFO_ A biologist trying to identify a group of unusual animals which are said to represent a new species begins by collecting all possible information about their appearance and behavior. After he has determined their typical size, shape, color, mode of reproduction, manner of locomotion, etc., he compares these characteristics with those of animals of known species and eventually classifies the strange specimens. In a similar way the professional investigator of UFO phenomena begins by asking the question: What is a typical unidentified flying object? The published reports comprise a heterogeneous collection of facts, fiction, and guesses. The investigator must first separate and discard accounts that are obvious hoaxes or delusions. There are many of these. The remaining material he divides into two classes. The first includes statements made by competent, careful witnesses, describing what they have seen and heard--for example, “I saw a brilliant light moving swiftly without sound.” The second class includes statements of opinion or belief about the thing seen--for example, “The strange light obviously was controlled by intelligence.” Putting aside this second class of material for the time being, he looks at the information in the first and immediately faces an awkward conclusion: apparently no “typical” flying saucer exists. _Descriptions of UFOs_ No two reports describe exactly the same kind of UFO. There are dozens of types of saucers, resembling each other as little as turnips do comets. Hoping to find some consistent pattern, the investigator opens his notebook and starts listing the data. _Shape_--The flying saucer varies greatly in shape (see Figure 1). At different times and places it may be a circular disk like a saucer, often with a small protrusion in the center like the knob on a tea-kettle lid; elliptical or bean-shaped like a flattened sphere; a circular base supporting a dome-like superstructure; a sphere surrounded by a central platform, like Saturn in its rings; long and thin like a cigar; a tapered sphere like a teardrop; spindle-shaped, with or without knobs on the ends; or a double- or triple-decked form like a stack of plates. _Size_--The saucer varies greatly in size. Estimated diameters range from 20 or 30 feet to several thousand. While under observation it may instantaneously increase or decrease in size. _Color_--The saucer varies greatly in color. It may be white, black, gray, red, blue, green, pink, yellow, silver; may be luminous or dull; may be a solid color; may be circled by a central band of different color; may display flashing lights of various colors. It may change color or luminosity while being observed.