See Chap. iii, sec. 2 a).
Luke 4 : 31 b.

XIII. Italicize letters used to designate quantities, lines, etc., in algebraic, geometrical, and similar matter, and in explanation of diagrams and illustrations.

(a+b)2=a2+2ab+b2; the line a c=the line a b; the nth power; at the point B.

XIV. Italicize particular letters of the alphabet when referred to as such.

We use a much more frequently than q.

XV. Authorities in science differ in the use of italics and capitals. In strictly scientific matter it is better to follow copy if the copy is intelligently prepared; if not, follow some recognized text-book on the subject.

In general the following rules will be found serviceable.

  1. In botanical, zoological, geological, and paleontological matter, italicize scientific (Latin) names of genera and species when used together (the generic name being in the nominative singular), and of the genera only, when used alone. When genera and species are used together the genus always comes first, species second.
  2. Agaricus Campestris, Felis leo, Conodectes favosus, Phyteuma Halleri, Pinus, Basidiabolus, Alternaria, Erythrosuchus.
  3. In medical matter the general practice is to print names of diseases and remedies in roman. In the Encyclopedia Britannica, Eleventh Edition, however, the scientific names of diseases are printed in italics.
    1. The lower-case letters designating certain Fraunhofer lines: a, b, g, h.
    2. The lower-case letters used by Baeyer to designate certain stars in constellations for which the Greek letters have been exhausted: f, Tauri; u, Hercules.
  4. In astronomical and astrophysical matter italicize:
    1. Greek, Latin, and Arabic names of planets, satellites, constellations, and individual stars: Neptune, Thetys, Orionis.
    2. Symbols for chemical elements: H. Ca. Ti.
    3. Capital letters given by Fraunhofer to the lines of the spectrum: A–H, K.
    4. Letters designating the special types of stars: A 5, B 3, Mb.
    5. The capital letter H with different Greek subscript letters, used to designate symbols of hydrogen: Ha, Hb, etc.
    6. Designations of celestial objects in well-known catalogues; also the Flamstead numbers:
    7. M 13 (for No. 13 of Messier's Catalogue of Nebulae and Clusters), Bond 619; N. G. C. 6165; B. D.-18° 4871; 85 Pegasi, Lalande 5761.
    8. But when initials are used to express the titles of catalogues, as such, and not to designate a particular celestial object, such initials are to be italicized, following the usual rule of references by titles.
    9. B. D.; N. G. C.
  5. Italic should not be used for:

Agaricus Campestris, Felis leo, Conodectes favosus, Phyteuma Halleri, Pinus, Basidiabolus, Alternaria, Erythrosuchus.

M 13 (for No. 13 of Messier's Catalogue of Nebulae and Clusters), Bond 619; N. G. C. 6165; B. D.-18° 4871; 85 Pegasi, Lalande 5761.