Tactile and emission theories of light

In its inherent simplicity, the tactile theory is able to describe the unknown in terms of the known. The mystery of vision is directly related to the simpler and more obvious sense of touch. The theory does, however, experience some 

Some of these difficulties of the tactile theory can be explained away by postulating that the visual probes are able to feel only certain kinds of surfaces and then making a series of assumptions that surfaces can be modified under various conditions. But this approach only ends up making the theory intolerably complicated, since the simple sense of relation to die sense of touch— the very important attribute of the theory—is lost. These conflicts can be resolved in a simple and satisfactory way by the emission theory if it is assumed that some bodies are able to emit a radiation to which the eyes are sensitive, and that others are able to reflect or scatter this radiation so that it enters the eye. For these and similar reasons, the tactile theory was gradually superseded by and eventually replaced with the emission theory. The process for this transformation was, however, very slow, and it was not until about 1000 AD that, under the influence of the Arabian astronomer Alhazen (discussed below), the tactile theory was finally abandoned.  

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