Reverted inverted

TM 9-258

Reverted inverted - See inverted image.

the line of sight to a limited degree. See correction

Rhomboidal prism - A prism with two pairs of parallel

wedge, measuring wedge.

sides forming right angles and two 45ƒ slanting or

Rouge - A material for polishing optical glass made

principally from red oxide of iron. The name is also

oblique parallel ends. It will displace the path of light

applied to polishing materials which are not red, such as

entering its ends without changing the direction of light.

black rouge and white rouge.

It does not invert or revert the image (fig 4-12).

Sclera - The outer of the three coats or tunics of the

Rhomboidal prisms may be rotated to divert the lines of

eyeball. It is tough, white, and flexible and is the white

sight to permit interpupillary adjustment of the eyepieces

portion of the eye normally seen. The slightly protruding

of a binocular instrument.

transparent portion of the center front of the eye, the

Right-angle prism - A type of prism used to turn a

cornea, is part of this coat (fig 3-2).

beam of light through a right angle (900) (fig 2-36). It will

Second - A unit of measurement of an angle equal to

invert (turn upside down) or revert (turn right or left),

one-sixtieth of a minute or 1/3600th part of a degree.

according to position of the prism, any light reflected by

Selective absorption - See absorption.

it. This prism is likewise used to turn a beam of light

through an angle of 180ƒ (fig 2-43) when either a normal

Selective reflection - See absorption.

Selective transmission - See absorption.

erect image or inverted, reverted image is produced,

Separator - Also known as spacer. A hollow tubular

depending upon the position of the prism with respect to

part used to separate two lenses at a definite distance

the object and the observer.

(fig 4-35).

Sighting instruments - Devices or instruments

designed to aid in the pointing of a weapon, observation

and azimuth or range determination, and looking over

obstacles.

Sine - The sine of an angle is the side of a right-

angle triangle opposite the angle divided by the

hypotenuse (the long side opposite the right angle).

Site Location - See angle of site.

Soft coat - A term designating the soft coating

applied to coated optics to differentiate between the

harder and more durable coating of magnesium fluoride

known as hard coat.

Spacer- See separator.

Spectrum - The band of colors produced by a prism

in dividing white light into its components.

The rainbow is an example, dispersion produces this

spectrum. See electromagnetic spectrum.

Spherical aberration - The aberration of a lens which

results when rays of light which pass through a lens near

its edge are converged to a point nearer the lens than

those rays passing through near the center (fig. 2-55).

Figure B-28. Right-angle prism .

The effect is poor definition of the image.

Split field - The field of view as seen when observing

Rod - One of the two types of light-sensitive

through a coincidence range finder. It is formed by

elements or visual cells in the retina of the eye which

uniting halves of the images produced by two objectives.

permit sight. The rods are associated with night vision

The half images are separated by the halving line.

and sight under other conditions of weak light. They also

Squint - See strabismus.

detect motion. For seeing in weak light, they are

Stadia scale - Graduations on a reticle which in

stimulated by a substance known as visual purple. The

conjuction with a rod of definite length can be used to

other type of visual cell is termed the cone (fig 3-5).

measure distances.

Roof-angle prism or roof prism - See Amici prism.

Standard candle - Initially a sperm whale oil candle,

Rotating prism - See Dove prism and Pechan prism.

7/8 inch in diameter, burning at the rate of 120 grains per

Rotating wedge - A circular optical wedge mounted

hour. Current standards of candle power are electric

to be rotated in the path of light to divert

lamps.

B-28