The term "fish-eye" actually predates the lens of that name. Physicist R.W. Wood presented the term in a 1906 article, "Fish-Eye Views and Vision Underwater." The hobby of keeping fish as pets was booming, thanks to the development of early home aquariums, and Wood offered a scientifically based description of how pet fish might view the world outside their glass tanks [sources: Kingslake; Lomography].
To understand what Wood described, take a chopstick and stick it into a glass of water. The straight piece of wood will appear to bend where it enters the liquid; this is an illusion caused by refraction, light bending as it goes form one medium (air) to another (water). This is the fundamental phenomenon that allows a fisheye lens to reach far to the sides of a scene and pull in the visual information at the edges of the frame.
Whereas a rectilinear lens is designed to behave like a window as light moves as straight as possible through its series of elements, the fisheye lens uses its elements like a funnel, bending a wide angle of light captured by the extremely curved outer element of the lens toward the film or sensor inside the camera. The fisheye's signature distortion comes from this funnel-shaped path: Light at the edges of the frame has to bend further to reach the film or sensor, resulting in greater distortion [sources: Atkins; Kingslake].
Lens maker Beck of London produced the first fisheye lens, labeled a "whole-sky lens," in 1924 for meteorologists and astronomers. As the name implied, the lens was intended to capture wide swaths of the sky in one shot. Scientists could then use geometric principles to account for the distortion, allowing them to measure the distances between and sizes of objects captured in the image. Other manufacturers followed suit over the next several decades, producing lenses with wider angles of view and greater clarity, with Nikon releasing the first interchangeable fisheye lens for 35mm cameras in 1962. This lens measured 8mm (the focal length) with an F/8 (the maximum aperture, or how wide the shutter can open to allow light through to the camera's film or sensor), and it brought fisheye photography to the consumer market. Hobbyists and professionals alike began to explore artistic ways to make use of this lens' signature distortion [source: Lomography].