the blue end [Greek: p] of the Image [Greek: pt], and which therefore suffer the greatest Refraction in the first Prism, are again in the second Prism more refracted than the rest. [Illustration: FIG. 16.] [Illustration: FIG. 17.] The same thing I try'd also by letting the Sun's Light into a dark Room through two little round holes F and [Greek: ph] [in _Fig._ 17.] made in the Window, and with two parallel Prisms ABC and [Greek: abg] placed at those holes (one at each) refracting those two beams of...