Pl. axes. [a. L. axis axle, axle-tree, pivot, axis of the earth, heavens, etc., cogn. with OE. eax: see AX sb.2 Used for various figurative and transferred senses of AXLE.]
I. Axis of rotation or revolution.
1. The axle of a wheel. ? Obs.
Wheel and axis, axis in peritrochio: the Wheel-and-Axle, one of the mechanical powers.
a. 1619. Fotherby, Atheom., II. xi. § 1. The weightines of the wheele doth settle it vpon his Axis.
1725. Bradley, Fam. Dict., s.v. Windmill, Like unto the Axis of a Cutlers Grind-Stone.
1796. Hutton, Math. Dict., I. 178. To construct an axis in peritrochio.
1822. Imison, Sc. & Art, I. 37. The wheel and axis may be considered as a kind of perpetual lever.
b. fig. The ‘pivot’ on which any matter turns.
1860. Motley, Netherl. (1868), I. v. 169. The axis of the revolt was the religious question.
2. Phys. a. A tooth or process on the second cervical vertebra, upon which the head is turned. b. The vertebra which has the process.
1694. Salmon, trans. Diemerbroeck’s Anat., IV. xii. (1714), 249. Axis … is a name which rather befits the former vertebra, whose tooth resembles an Axle.
1701. Tauvry, Anat., II. xvi. 268. This second Vertebra has an Apophysis call’d the Tooth…. The Head and the first Vertebra, making but one piece, are qualified to turn upon that Axis.
1815. Encycl. Brit., III. 289. Axis … the second vertebra of the neck; it hath a tooth which goes into the first vertebra and this tooth is by some called the axis.
1836. Athenæum, No. 450. 419. The Atlas and Axis of the Ichthyosaurus are united.
3. The imaginary straight line about which a body (e.g., the earth or other planet) rotates; the prolongation of that of the earth on which the heavens appear to revolve.
(The ends of the axis are poles; thence the use of axis as a line from pole to pole, or from end to end: see III.)
1549. Compl. Scot., vi. 48. Ȝe sal ymagyn ane lyne that passis throucht the spere lyik til ane extree of ane cart, callit axis spere.
1635. N. Carpenter, Geogr. Del., I. iii. 67. The motion of an iron-wire or needle … vpon his owne Axis.
c. 1660[?]. Hobbes, Physics, IV. xxvi. § 6. I. 428. The earth is so carried about the sun, as that its axis is thereby always kept parallel to itself.
1849. Mrs. Somerville, Connex. Phys. Sc. There are at least three axes at right angles to each other round any one of which … the solid … will continue to revolve for ever.
† 4. fig. A central prop, which sustains any system (as Atlas was feigned to sustain the revolving heavens). Obs.
a. 1616. Beaum. & Fl., Valentin., V. v. I have found out axis; You know he bears the empire.
1646. Sir T. Browne, Pseud. Ep., 94. The Atlas or maine axis, which supported this opinion, was daily experience.
5. The geometrical line, by the revolution of a superficies about which, solids with circular section, as a globe, cylinder, cone, etc., are conceived to be generated.
(This is the axis of revolution; it coincides necessarily with the axis of symmetry; thence branch II.)
1571. Digges, Pantom., III. iii. Q ij b. The Axis or Altitude of the Cone.
1796. Hutton, Math. Dict., I. 177. If a semicircle be moved round its diameter at rest, it will generate a sphere, whose axis is that diameter.
II. Axis of symmetrical arrangement. (Cf. 5.)
6. The straight line about which the parts of a body or system are symmetrically arranged.
Axis of a balance: the line upon which it turns. Axis of oscillation (of a pendulum, etc.): a horizontal line passing through the centre of the oscillation, and perpendicular to its plane (Hutton, 1796). Axis of polarization: the central line round which the prismatic rings or curves are arranged. Neutral axis (of a girder): the line where there is neither compression nor tension (Brewster).
7. Geom. Any line in a regular figure which divides it into two symmetrical parts, e.g., which joins opposite angles or the centers of opposite sides; in a conic section, the line from the principal vertex or vertices, perpendicular to the tangent at that point; in a curve, a straight line which bisects a system of parallel chords (called principal axis when it cuts them at right angles).
Transverse axis (in the ellipse and hyperbola): that which passes through the two foci; conjugate axis, that which bisects the transverse one at right angles. The axes of an ellipse are also called major and minor.
1734. Builder’s Dict., Axis of a Conic Section, is a quiescent Right Line passing through the Middle of the Figure, and cutting all the Ordinates at Right Angles.
1796. Hutton, Math. Dict., I. 177. Axis … more generally … a right line conceived to be drawn from the vertex of a figure to the middle of the base. Ibid. The ellipse and hyperbola have each two axes; but the parabola has only one, and that infinite in length. Ibid. In curves of the second order, that diameter whose parallel ordinates are at right angles to it, when possible, is an Axis.
1849. Mrs. Somerville, Connex. Phys. Sc., xxi. 201. Cut longitudinally, that is, parallel to the axis of the prism.
1853. Sir J. Herschel, Pop. Lect. Sc., iii. § 13 (1873), 106. The longer axes or longest dimensions of their orbits.
1879. Thomson & Tait, Nat. Phil., I. I. § 120.
8. Crystallog. An imaginary line drawn between the centers of opposite faces or edges, or the apices of opposite angles. (See quot.)
1817. R. Jameson, Charac. Min., 244. Three of the cleavages are equiangular and oblique-angular, in a common axis.
1869. Roscoe, Elem. Chem., 192. In order to classify … crystals, the existence of certain lines within the crystal called axes is supposed, round which the form can be symmetrically built up.
1878. Gurney, Crystallog., 30. The straight lines or directions in the crystal which are common to two or more symmetral planes are called axes of symmetry.
9. Optics. a. A ray passing through the center of the eye or of a lense, or falling perpendicularly on it; the line that passes through the centers of the lenses in a telescope; the straight line from the eye to the object of sight.
1701. Tauvry, Anat., II. vii. 205. They serve to direct the two Optick Axis’s, in looking upon the same Object when it moves round.
c. 1790. Imison, Sch. Art, I. 196. If the axis of both eyes are not directed to the object, that object will appear double.
1831. Brewster, Optics, iv. 28. In all these lenses a line … passing through the centres of their curved surfaces, and perpendicular to their plane surfaces, is called the axis.
1855. H. Spencer, Psychol. (1872), I. III. x. 380. Due convergence of the visual axes.
1871. J. Dicksee, Perspective, 27. The axis of vision or line of direction is an imaginary line proceeding from the spectator to the perspective centre.
b. Axis of incidence: the line passing through the point of incidence perpendicularly to the refracting surface. Axis of refraction: the continuation of the same line through the refracting medium. Axis of double refraction: the line or direction on both sides of which double refraction takes place, but along which it does not exist.
1734. Builder’s Dict., Axis of Incidence, Refraction.
1796. Hutton, Math. Dict., I. 178.
1831. Brewster, Optics, xvii. 147. An axis of double refraction … is not like the axis of the earth, a fixed line within the rhomb or crystal. It is only a fixed direction.
1836. Athenæum, No. 448. 381. Like calcareous spar it has one axis of double refraction.
¶ In the three following the sense tends to pass into axis of growth or direction as in branch III.
10. Phys. and Zool. The central core of an organ or organism; the central skeleton or nervous cord; the central stem or core round which polypes grow; the central column of a whorled shell.
1741. Monro, Anat. Bones, 54. The Powers that draw it towards the Axis of the Bone.
1830. Edin. Encycl., XIV. 599. In other species, the organs, which are not in pairs, are arranged round a central axis.
1866. R. Tate, Brit. Mollusks, iii. 44. The axis of the shell around which the whorls are coiled.
1873. A. Flint, Nerv. Syst., ix. 257. The nervous matter contained in the cavity … is known as the cerebrospinal axis.
11. Bot. a. The central column of the inflorescence or other whorl of growth. b. The main stem and root.
1786. Rees, Encycl., Axis … a taper column placed in the centre of some flowers, or katkins, about which the other parts are disposed.
1835. J. Comstock, Yng. Botanist, 239. Axis, centre of vegetation, as the pith of vascular plants.
1835. Penny Cycl., III. 184. Each cluster of leaves is a small branch without perceptible axis.
1857. Henfrey, Bot., § 42. 21. The stem is the ascending portion of the axis of a plant.
1870. Hooker, Stud. Flora, 232. Erica … Seeds attached to a central axis.
12. Physiogr. and Geol. A central ridge; the central line of a valley.
Anticlinal axis: the line along which two opposite planes of stratification meet in a ridge. Synclinal axis: the line along which they meet in a depression.
1830. Lyell, Princ. Geol., I. 135. A line of volcanos … parallel to the axis of the older ridge.
1849. Murchison, Siluria, ii. (1867), 25. These round-backed hills … rise boldly from beneath the surrounding Silurian deposits, of which they form the axis.
1854. F. Bakewell, Geol., 4. The technical name given to such a centre of elevation is the ‘anticlinal axis.’
III. A straight line from pole to pole (cf. 3), or from end to end, of any body.
13. gen. e.g., Axis of the equator: the polar diameter of the earth, which is also the axis of rotation; see 3. Axis of the ecliptic, of the horizon: a diameter of the sphere passing through these circles at right angles to their planes.
1796. Hutton, Math. Dict.
14. spec. An imaginary line uniting the two poles of a magnet.
1664. Power, Exp. Philos., III. 158. If you divide the Magnet through a meridian, or Saw of a Segment, parallel to the Axis.
1832. U. K. S., Nat. Philos., II. Magnetism, i. § 6. The straight line joining the two poles of a magnet is called its axis.
15. A main line of motion, growth, extension, direction.
1818. W. Lawrence, Nat. Hist. Man, I. ii. (1848), 99. Its axis [of the femur] coincides with the centre of gravity of the body.
1853. Kane, Grinnell Exp., x. (1856), 75. The axis of Baffin’s Bay … is from the north by east. Ibid., 76. The ice, after changing its original axis of drift.
1855. Owen, Skel. & Teeth, 6. In the direction of the bone’s axis.
1867. A. Barry, Sir C. Barry, vii. 240. The principal axis of the building.
IV. Axis of reference.
16. Analyt. Geom. Each of the two intersecting straight lines, by reference to which the position of a certain point, the locus, is determined.
(Transf. from the geometrical treatment of conic sections.)
1855. Todhunter, Plane Co-ord. Geom.
V. Comb. Axis-cylinder (or axis-band), see quot.; attrib., as axis-ligament.
1839. Todd, Cycl. Anat. & Phys., III. 592/1. A central substance of nervous matter … the axis-cylinder of Rosenthal.
1855. H. Spencer, Psychol. (1872), I. I. ii. 27. The central fibre, or axis-cylinder of a nerve tube.
1877. Rosenthal, Muscles & N., 104. The axis-band, or axis-cylinder.
1877. Burnett, Ear, 72. In all its motion as a lever the hammer swings about this axis-ligament as a fixed point.
