[Subst. use of next. Cf. F. spirale fem. (also spiral masc., spiral spring), It. spirale.]
1. Geom. A continuous curve traced by a point moving round a fixed point in the same plane while steadily increasing (or diminishing) its distance from this.
Spiral of Archimedes, a curve traced by a point moving uniformly along a line which at the same time revolves uniformly round a fixed point in itself. Equiangular, Hyperbolic, Logarithmic, Loxodromic, Parabolic spiral: see these words.
1656. trans. Hobbes’ Elem. Philos., xvii. 194. The description of Archimedes his Spiral, which is done by the continual diminution of the Semidiameter of a Circle in the same proportion in which the Circumference is diminished.
1697. Dryden, Virg. Georg., Ded. (1721), I. 179. At that time the Diurnal Motion of the Sun partakes more of a Right Line than of a Spiral.
1728. Chambers, Cycl., s.v., Then will the Points M m, m, &c. be Points in the Spiral, which connected, will give the Spiral itself.
1816. C. Babbage, trans. Lacroix’ Different. & Integr. Calculus, 128. The spirals compose another class of transcendental curves.
1869. Rankine, Machinery & Millwork, 54. Each point in the secondary piece … describes a plane spiral about the fixed axis.
1882. Minchin, Unipl. Kinemat., 50. Prove that the Space Centrode is a parabola and the Body Centrode a spiral of Archimedes.
fig. 1845–6. Trench, Huls. Lect., Ser. I. iv. 57. The advance may sometimes be rather in a spiral than in a straight line.
1848. H. Rogers, Ess. (1874), I. vi. 319. Other questions succeed,… gradually approaching in one long spiral of interrogations the central position.
2. A curve traced by a point moving round, and simultaneously advancing along, a cylinder or cone; a helix or screw-line.
The spiral has sometimes been distinguished from the helix: see quot. 1728.
1670. Collins, in Rigaud, Corr. Sci. Men (1841), I. 147. The spiral described by the compound motion of a heavy body falling to the centre of the earth.
1681. trans. Willis’ Rem. Med. Wks., Vocab., Spiral, a turning about, and as it were ascending.
1728. Chambers, Cycl., Spiral, in Architecture, Sculpture, &c. is a Curve that ascends, winding about a Cone…. By this it is distinguished from the Helix, which winds … around a Cylinder.
1788. New Lond. Mag., 44. The length of the Spiral described by the fly in passing from one pole to the other.
1835. Mrs. Somerville, Connex. Phys. Sci. (ed. 2), xvii. 172. By thus tracing these nodal lines he discovered that they twist in a spiral or corkscrew round rods and cylinders.
1876. Voyle & Stevenson, Milit. Dict., 198/2. Increasing Spiral, a term applied to the twist or the spiral inclination of the grooves of rifled arms.
b. The degree in which the successive circles of such a curve approach each other.
1846. Greener, Sci. Gunnery, 348. From the peculiar nature of the powder … the extreme spiral given to their grooves was required.
1864. Daily Tel., 1 Aug., 3/2. Where the breech-loading principle is good, making the arm shoot well, is simply matter of detail, involving considerations of length of barrel, character and spiral of rifling, and suitability of ammunition.
3. a. A piece of wire coiled into a spiral form.
1825. Annals Philosophy, X. 52. After which the extremity of the spiral being tied hard,… I put the covered wire in a vice.
1881. J. Hatton, New Ceylon, vi. 154. Men and women alike wear the neck spiral, and the former also a closely-fitting spiral around their biceps.
1885. C. G. W. Lock, Workshop Rec., Ser. IV. 298/2. The spirals of the key-board must be bent their right shape.
b. Bot. A spiral vessel in plants.
1837. P. Keith, Bot. Lex., 241. According to Raspail it is composed of cells, tubes, and spirals yet visible. Ibid., 288. They have neither stomata nor spirals: hence they can neither form the green chromule, nor exhale moisture.
c. Astr. A spiral nebula.
1866. Lockyer, Guillemin’s Heavens, 400. Brilliant spirals, unequally luminous,… diverge from the centre, and become separated … as they recede from it.
1881. G. F. Chambers, Smyth’s Celestial Cycle, 38. One of Lord Rosse’s ‘spirals.’
d. In general use: Any object having a spiral form.
1853. G. P. R. James, Agnes Sorel, I. i. 19. The staircase was merely one of those narrow, twisting spirals, which we rarely see, except in Cathedrals or ruined castles, in the present times.
1858. Lardner, Hand-bk. Nat. Phil., 119. In practice, the spiral through which the water is carried is not in the form of a tube.
1883. C. H. Farnham, in Harper’s Mag., Aug., 375/2. Misfortune awaits the boat that ventures into this watery spiral.
1890. J. Cagney, trans. Jaksch’s Clin. Diagnosis, iv. 70. The spirals are often overlaid with epithelium.
4. One of the separate circles or coils of a spiral or helical object. Cf. SPIRE sb.3 1.
1728. Chambers, Cycl., s.v. Screw, The said Distance between the Spirals … of the Screw.
c. 1790. Imison, Sch. Arts, I. 23. Supposing the distance of the spirals to be half an inch.
1825. J. Nicholson, Operat. Mechanic, 240. If, therefore, a pipe of uniform bore be wrapped round a conic frustrum,… the spirals will be very nearly such as will answer the purpose.
1891. Kipling, Light that Failed (1900), 272. He stroked the creaseless spirals of his leggings.
