# COBBLE

A stone particle between 64 and 256 millimeters (about 2.5 to 10 inches) in diameter

## Related Terms

### HARMONIC MOTION

The projection of circular motion on a diameter of the circle of such motion. Simple harmonic motion is produced if the circular motion is of constant speed. The combination of two or more simple harmonic motions results in compound harmonic motion.

### BORE

Inside diameter of a cylinder.

### ICE FOG

Fog composed of suspended particles of ice, partly ice crystals 20 to 100 microns in diameter but chiefly, especially when dense, droxtals 12 to 20 microns in diameter. It occurs at very low temper- atures, and usually in clear, calm weather in high latitudes. The sun is usually visible and may cause halo phenomena. Ic

### TACTICAL DIAMETER

The perpendicular distance between a ship's course when the helm is put hard over and her course when she has turned through 180 degrees; the ratio of the tactical diameter divided by the ship's length between perpendiculars gives a dimensionless parameter which can be used to compare the manoeuverability of ships.

### APERTURE

1. An opening; particularly, the opening in the front of a camera through which light rays pass when a picture is taken. 2. The diameter of the objective of a telescope or other optical instrument, usually expressed in inches, but sometimes as the angle between lines from the principal focus to opposite ends of a diameter of the or a this line represents the intersection of the appropriate datum with the outer limits of vegetation and appears to the navigator as the shoreline

### APERTURE RATIO

The ratio of the diameter of the objective to the focal length of an optical instrument

### ATOLL

A ring-shaped coral reef which has closely spaced islands or islets on it enclosing a central area or lagoon. The diameter may vary from less than a mile to 80 or more.

### MAJOR AXIS

The longest diameter of an ellipse or ellipsoid.

### COMPOUND HARMONIC MOTION

The projection of two or more uniform circular motions on a diameter of the circle of such motion. The projection of a simple uniform circular motion is called SIMPLE HARMONIC MOTION.

### METEOR

The phenomenon occurring when a solid particle from space enters the earth’s atmosphere and is heated to incandescence by friction of the air. A meteor whose brightness does not exceed that of Venus (magnitude -4) is popularly called SHOOTING STAR or FALLING STAR. A shooting star results from the entrance into the atmosphere of a particle having a diameter between a few centime- ters and just visible to the naked eye. Shooting stars are observed first as a light source, similar to a star, which suddenly appears in the sky and moves along a long or short path to a point where it just as suddenly disappears. The brighter shooting stars may leave a trail which remains luminous for a short time. Meteors brighter than magnitude -4 are called BOLIDES or FIREBALLS. Light bursts, spark showers, or splitting of the trail are sometimes seen along their luminous trails which persist for minutes and for an hour in exceptional cases. The intensity of any meteor is dependent upon the size of the particle which enters the atmosphere. A particle 10 centimeters in diameter can produce a bolide as bright as the full moon.

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