sphere of influence

An area of the world dominated politically or economically by a country, or certain countries.

sphere of reflection

In crystallography, a construction for considering conditions for diffraction in terms of the reciprocal rather than the real lattice.

It is a sphere with the incident beam along a diameter. The origin of the reciprocal lattice is positioned at the point where the incident beam emerges from the sphere.

Whenever a reciprocal lattice point touches the surface of the sphere, the conditions for a diffracted (or reflected) beam are satisfied.

sphere photometer, integrating-sphere photometer

An instrument for measuring the total luminous flux of a lamp or luminaire; the source is placed inside a sphere whose inside surface has a diffusely reflecting white finish, and the light reflected from this surface onto a window is measured by an ordinary photometer.

spheres of Eudoxus

A theory of Eudoxus from about 400 B.C.; a cosmological theory in which the planets, the sun, and the moon were described as being carried on a series of concentric spheres rotating within one another on different or various axes.

Eudoxus of Cnidus (about 408 B.C. to 347 B.C.) was a Greek astronomer and mathematician.

spheresthesia

(s) (**noun**), spheresthesias

(pl)
An apparent sensation of a ball or globe that rises in the stomach area and progresses upward, finally being felt in the throat where it produces the feeling of strangulation; as seen in hysteria: Mary, the heroine in the novel, was seized by *spheresthesia* as her fear mounted until she felt as if she were being strangled.

1. Having or nearly having the shape of a sphere; that is, rounded, globular, global, or round like a ball or globe.

2. Of or concerning a sphere, or formed on the surface of a sphere; such as, a geometric figure.

3. Of or concerning heavenly bodies regarded astrologically as exerting influence on human nature and events.

4. Referring to the heavenly bodies, or to their supposed revolving spheres or shells.

spherical aberration

1. An aberration arising from the fact that rays which are initially at different distances from the optical axis come to a focus at different distances along the axis when they are reflected from a spherical mirror or refracted by a lens with spherical surfaces.

2. A fault in a lens or curved mirror in which light passing through the edge has a different focal point from light passing through the center, resulting in blurred images.

3. The blurring of an image that occurs when light from the margin of a lens or mirror with a spherical surface comes to a shorter focus than light from the central portion.

The changing focal length is caused by deviations in the lens or mirror surface from a true sphere.

spherical antenna

In electromagnetism, an antenna having the shape of a sphere, used primarily in theoretical studies.

spherical astronomy

The branch of astronomy dealing with positions on the celestial sphere.

spherical capacitor

A capacitor made of two concentric metal spheres with a dielectric filling the space between the spheres.

spherical coordinates, spherical polar coordinates, geographical coordinates

1. A system of curvilinear coordinates (co-ordinate system composed of intersecting surfaces) in which the position of a point in space is designated by its distance from the origin or pole, called the radius vector, the angle φ between the radius vector and a vertically directed polar axis, called the cone angle or co-latitude, and the angle θ between the plane of φ and a fixed meridian plane through the polar axis, called the polar angle or longitude.

2. A set of coordinates used for locating a point in space, representing its distance from an origin and two angles describing its orientation relative to perpendicular axes extending from that origin.

3. A system of coordinates for locating a point in space by the length of its radius vector and the angles this vector makes with two perpendicular polar planes.

spherical cyclic curve, cyclic curve

A curve; such as, a cycloid, cardioid, or epicycloid; generated by a point of a circle that rolls (without slipping) on a given curve.

It involves the intersection of a quadric surface with a sphere.

spherical degree

1. A solid angle equal to one-ninetieth of a spherical right angle.

2. A unit of relative surface area for spheres, equal to 1/720 the total surface area.

Thinking in terms of the earth's surface, this is the area of the region in one hemisphere (northern or southern) bounded by the equator and two meridians of longitude one degree apart.

spherical geometry, spherics

The geometry of circles, angles, and figures on the surface of a sphere.

spherical mirror

1. A mirror, either convex or concave, whose surface forms part of a sphere.

2. A curved reflective surface, which may be either convex, bulging outwardly; or concave, bulging inwardly.

Most curved mirrors have surfaces which are shaped like part of a sphere, but other shapes are sometimes used in optical devices, too.

Related **ball, sphere**-word units:
**glob-, glom-**;
**hemoglobin-**.