Radiata, b. [478].

Radiation, b. [139].

Rays, b. [58].

Realists, a. [238].

Refraction, b. [54].

Refraction of heat, b. [155].

Remora, a. [190].

Resinous electricity, b. [195].

Rete mirabile, b. [463].

Retrograde motion of planets, a. [139].