Parallax, a. [159].
Percussion, Centre of, a. [357].
Perfectihabia, a. [75].
Perigee, a. [146].
Perijove, a. [446].
Periodical colors, b. [93].
Phases of the moon, a. [134].
Philolaic tables, a. [304].
Phlogisticated air, b. [273].
Phlogiston, b. [268].