- Gravity
- Green, N. E
- Gulf of the Titans (See Sinus Titanum)
- Hades, the
- Hammonis Cornu, neck between it and Hellas
- Heat
- Hellas
- Hesperia
- Hourglass Sea, the
- Huyghens, drawing of Mars
- Hydrogen
- Ice, particles of, in Martian air
- Ice-cap (See Polar cap, and South polar cap.)
- Indus, the, first seen
- Inhabitants, of Mars
- Inhabitants, of Mars
- Inhabitants, of Mars
- Inhabitants, of Mars (and pages following this)
- Irregularities, on terminator, not mountainous
- Irrigation