on the Affections and Properties of Light. 385 
Proposition V. All the consequences deducible from the 
theory a priori are found to follow in fact. 
Proposition VI. The common fringes by flexion (called 
hitherto the “ three fringes”), are found to be as numerous as 
the others. 
Proposition VII. The unusual image by Iceland crystal is 
caused by some power inherent in its particles, different from 
refraction, reflexion, and flexion. 
Proposition VIII. This power resembles refraction in its 
degree of action on different rays ; but it resembles flexion 
within the body, in not taking place at a distance from it, in 
acting as well on perpendicular as on oblique rays, and in its 
sphere or space of exertion moving with the particles which it 
attends. 
