gnomon

Noun

gnomon (plural gnomons)

1. An object such as a pillar or a rod that is used to tell time by the shadow it casts when the sun shines on it, especially the pointer on a sundial.
   • Let a Gnomon, being firſt ſharpened into a Point, be ſhaped, and faſtned in ſuch wiſe, that it no way hinder either the draught of the Horizontal Line, or the Point of the ſhadow from having free access to the Dial at all times of the Year. […] Upon the Superfices of the Dial, obſerve the Point of...1700, Samuel Foster, “[Projective Dialling: … The Ninth Tractate. Appendix.] Chap. IV. A General and Most Easie Way to Project Hour-lines upon All Kinds of Superfices without any Regard had to Their...
   • The moſt celebrated gnomons, for examining the courſe of the ſun, which are exiſting at this time, have been ſuppoſed to be that in the church of St Petronio at Bologna, 89 Engliſh feet high; that of the Chartreux at Rome, about 67 feet; and that of St Sulpice at Paris, 86 feet. […] [T]he gnomon of...1758 March, “An Account of an Ancient Astronomical Instrument, of Immense Dimensions, lately Restored to Use”, in Sylvanus Urban [pseudonym; Edward Cave], editor, The Gentleman’s Magazine, and...

   Synonyms:

   cock, style

2. An object such as a pillar used by an observer to calculate the meridian altitude of the sun (that is, the altitude of the sun when it reaches the observer's meridian), for the purpose of determining the observer's latitude.
   • This muſt be performed by help of a Spherick Gnomon, (as Blaew [Willem Janszoon Blaeu] calls it,) which is a ſmall Pin or Needle fixed perpendicularly into a ſmal Baſis with an hollow concave bottom, that it may ſtand upon the convexity of the Globe.1659, Joseph Moxon, “Prob[lem] XVIII. Another Way to Find the Height of the Pole by the Globe; if the Place of the Sun be Given; and also to Find the Hour of the Day, and Azimuth, and Almicantar of...
   • In order to aſcertain the latitude of any place, the ancients obſerved the meridian altitude of the ſun, either by means of the ſhadow of a perpendicular gnomon, or by means of an aſtrolabe, from which it was eaſy to compute how many degrees and minutes the place of obſervation was diſtant from the...1791, William Robertson, “Section II. Intercourse with India, from the Establishment of the Roman Dominion in Egypt, to the Conquest of that Kingdom by the Mahomedans”, in An Historical Disquisition...
3. The index of the hour circle of a globe.
   • Index of a globe, the little style or gnomon, which being fixed on the pole of the globe, and turning round with it, points out the hours upon the hour circle.1809, William Nicholson, “Index of a globe”, in The British Encyclopedia, or Dictionary of Arts and Sciences; […], volume III (E … I), London: Printed by C[harles] Whittingham, […]; for Longman...
4. A plane figure formed by removing a parallelogram from a corner of a larger parallelogram.
   • If a Parallelogram be divided into four leſſer ones, by two Lines interſecting each other; and one of theſe Parallelograms be retrench'd, or taken away; the other three will make a Gnomon, ordinarily call'd a Square.1728, E[phraim] Chambers, “Gnomon”, in Cyclopædia: Or, An Universal Dictionary of Arts and Sciences; […] In Two Volumes, volumes I (A–H), London: […] James and John Knapton [et al.], →OCLC, page 164...
5. (broadly) A number representing the increment between two figurate numbers (“numbers equal to the numbers of dots in geometric figures formed of dots”).
   • [page 16] The figurate number's gnomon is therefore 1#43;nb in the general case. A trivial family of numbers, those for which b#61;0, might be called linear. […] [page 17] Clearly, a figurate number of rank n is equal to the sum of its first n gnomons, and in particular the sum of the first n odd...1999, Midhat J. Gazalé, “Figurate and m-adic Numbers”, in Gnomon: From Pharaohs to Fractals, Princeton, N.J.; Chichester, West Sussex: Princeton University Press, →ISBN, pages 16 and 17