Rays became first of all totally reflected, which before at equal Incidences with the rest had suffered the greatest Refraction. And the same thing happens in the Reflexion made by the common Base of the two Prisms in the tenth Experiment. _PROP._ IV. PROB. I. _To separate from one another the heterogeneous Rays of compound Light._ [Illustration: FIG. 23.] The heterogeneous Rays are in some measure separated from one another by the Refraction of the Prism in the third Experiment, and in the fifth Experiment,...