_The returns of the disposition of any Ray to be reflected I will call its_ Fits of easy Reflexion, _and those of its disposition to be transmitted its_ Fits of easy Transmission, _and the space it passes between every return and the next return, the_ Interval of its Fits.
DEFINITION.
From Opticks: A Treatise of the Reflections, Refractions, Inflections and Colours of Light by Isaac Newton.
