Ice Age—use initial caps for the most recent glacial period, lower case for all other references (American Heritage Dictionary, Third Edition). [revised 2/00]
i.e.—not italicized; always set off by commas; stands for "id est" (that is)
imagery, satellite—see satellite-based imagery
initials—no space between two: T.N. Krishnamurti (this is contrary to The Chicago Manual of Style). See also "names."
in situ—not italicized, no hyphen as modifier; means "in position"
I/O—input/output (computer term)
instrument names—We now use initial caps for instruments and instrument systems: Limb Radiance Inversion Radiometer (LRIR), Advanced Coronal Observing System, S-Band Dual Polarization Doppler Radar (S-Pol), but S-Pol radar. [revised 2/00]
Internet addresses—Use roman, not bold or italic, for e-mail, Internet, and other electronic addresses.
Intermountain West—use this spelling [2/00].
ionization states—(series) are given by capital Roman numerals—Fe XI, Ba II, etc. Use a space (not a hyphen) between the element abbreviation and roman numeral. See complete list of chemical elements in The Chicago Manual of Style.
Iris Giclée—initial caps, accent like this [09-00]
isotope numbers—When you abbreviate these, put the number before the element: 13C, 90Sr, etc. In popular literature these are sometimes written this way: The isotope carbon 13 (C-13) [spellout is open, abbreviation takes a hyphen]. [revised 2/00]
italics—Try to reword rather than use italics for emphasis; use italics for emphasis only as a last resort.