Needle, dip of, [407]
Noise, how it differs from musical sound, [263]
Non-conductors of heat, [298]
Non-conductors of electricity, [375]
Notes, musical, how produced, [264]
Odors, minuteness of their particles, [19]
Order in nature, [65]
Papin's digester, [292]
Pendulum, [208-210]
Perpetual motion attempted, [118]