incidence
(ˈɪnsɪdəns)
[a. F. incidence (15th c.), f. incident incident a.1: see -ence.]
† 1. a. = incident n.1 1; incidental matter. Obs.
| 1423 Jas. I Kingis Q. vii, Procede I will agayn to my sentence Off my mater, and leue all Incidence. 1525 Ld. Berners Froiss. II. i. 3 In the same season there fell in Lombardye a marueylous insydence, which was moche spoken of throughe out all the worlde. Ibid. clii. [cxlviii.] 419, I knowe nat by what insydence certayne men layde in wayte on hym, and in the feldes set on him or he was ware. 1605 Bacon Adv. Learn. ii. viii. §3 Many operations have been invented sometimes by a casual incidence and occurrence. 1651 Jer. Taylor Holy Living iii. §4 (1870) 153 He that hath wounded his neighbour is tied to the expenses of the Surgeon and other incidences. |
† b. A casual circumstance. Obs.
| 1670 G. H. Hist. Cardinals ii. i. 111 Since by way of incidence [It. incidenza, digression], I have spoken of Alms. |
† c. = incident n.1 4 b. Obs.
| 1574 tr. Littleton's Tenures 47 a, Al the rente and service in suche case bee incidences to the reversion. |
† 2. Liability; natural tendency to. Obs.
| 1652 Gaule Magastrom. 112 A conscious and confest incidence to error..even in the very rule or art it self. |
3. The act or fact of falling upon, coming in contact with, or affecting in some way.
| 1656 Stanley Hist. Philos. iv. (1701) 135/2 It is enough that a Man be affected and reduced by incidence of one single pleasure. 1853 Kane Grinnell Exp. xxiv. (1856) 196 The great expanse..had up to this moment resisted the enormous incidence of a heavy gale. 1868 Rogers Pol. Econ. ix. (1876) 93 The incidence of the event will be very probably obviated by the large use of machinery in agricultural operations. 1885 J. Martineau Types Eth. Th. (ed. 2) I. i. xi. §8. 212 A partial incidence of the Divine thinking. |
4. Physics. The falling of a line, or anything moving in a line (as a projectile, a ray of light, heat, etc.) upon a surface; the manner of such falling, esp. in regard to the inclination of the line of incidence to the surface.
angle of incidence, (a) the angle which the incident line, ray, etc., makes with the perpendicular or normal to the surface at the point of incidence († formerly, also, the angle between the line, etc., and the surface); (b) the angle which the chord of an aircraft wing makes with the direction of the undisturbed air current. axis of incidence, the perpendicular or normal to the surface at the point of incidence. cathetus of incidence (see cathetus, quot. 1751). plane of incidence, the plane through the line of incidence and the normal to the surface. point of incidence, incidence-point, the point at which the line of incidence meets the surface. † ray of incidence, an incident ray, a ray which falls upon a reflecting or refracting surface.
| 1626 Bacon Sylva §245 In Mirrours, there is the like Angle of Incidence, from the Object to the Glasse, and from the Glasse to the Eye. 1656 tr. Hobbes' Elem. Philos. Wks. 1839 I. 274, I call an angle of incidence, that which is made between a strait line and another line, strait or crooked, upon which it falls, and which I call the line reflecting. 1658 Sir T. Browne Gard. Cyrus iv. 67 This is also the law of reflexion in moved bodies and sounds, which..observe the rule of equality between incidence and reflexion. 1664 Power Exp. Philos. i. 81 Every Ray of incidence is seven times refracted in the Eye before it reach the Retina. 1704 Newton Opticks (J.), In equal incidences there is a considerable inequality of refractions. 1727–41 Chambers Cycl. s.v. Axis, Axis of Incidence, in dioptrics, is a right line drawn through the point of incidence, perpendicularly to the refracting surface. 1803 J. Wood Princ. Mech. vi. 130 The velocity of the body after reflection is equal to it's velocity before incidence. 1854 Tomlinson Arago's Astron. 3 DO will be the direction of the reflected ray, and the point I, where it cuts the surface of the mirror, will be the point of incidence. 1871 Tyndall Fragm. Sc. (1879) II. viii. 129 The searcher welcomes every gleam, and seeks to augment his light by indirect incidences. 1908, etc. [see angle n.2 1 ¶ ]. 1948 Sci. News VII. 28 The pilot is able to increase or decrease the lift by altering the angle of incidence. Ibid., As the angle of incidence increases, the lift also increases and the aircraft is able to climb, but if the tilt is made too large the flow on the upper surface separates and eddies are formed. |
5. Astron. = immersion 3.
| 1727–41 Chambers Cycl. s.v. Eclipse, Immersion, or incidence of an eclipse, is the moment when part of the sun or moon's disk first begins to be hid. |
6. Geom. The situation of one locus with respect to another when they have a common point or points, but do not completely coincide; e.g. of a point to a line on which it lies, of a point or a line to a plane in which it lies, or of two intersecting lines to each other. [From the German of Schubert, Kalkul der Abzähl. Geom. (1879) 25.]
7. a. Manner of falling upon or affecting in any way; the range or scope of a thing, the extent of its influence or effects.
| 1846 Fonblanque in Life & Labours (1874) 210 It is clear that the Duke has not mistaken the post hoc for the propter hoc, incidence for causation. 1851 De Quincey Ld. Carlisle on Pope Wks. XIII. 24 The question..always is, Whether the differential feature..ought not to disturb the incidence of the legal rule? 1866 Rogers Agric. & Prices I. xv. 266 The incidence of the Plague was general. 1871 Earle Philol. Eng. Tongue §37 On, the preposition, exists in Saxon, but its area of incidence is different. |
b. spec. in Pol. Econ. Of taxation (see quot. 1878).
| 1825 M{supc}Culloch Pol. Econ. i. 8 The incidence and effect of taxes and regulations. 1848 Mill Pol. Econ. v. vi. §1 (1876) 521 The real incidence of indirect taxation is every day more generally understood. 1878 Jevons Prim. Pol. Econ. 127 It is often impossible to say what is really the incidence of a tax, that is, the manner in which it falls upon different classes of the population. |
8. Special Comb.: incidence wire Aeronaut., on a biplane (see quot. 1916).
| 1916 H. Barber Aeroplane Speaks 143 Incidence wire, a wire running from the top of an interplane strut to the bottom of the interplane strut in front of or behind it. It maintains the ‘stagger’ and assists in maintaining the angle of incidence. 1928 V. W. Pagé Mod. Aircraft v. 175 These wires are called ‘incidence wires’, as they keep the planes in the proper angular relation to each other. |