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U.S. Government Printing Office, 1929 - Meteorology

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Page 37 - Woolpack Clouds — Thick clouds of which the upper surface is dome-shaped and exhibits protuberances, while the base is horizontal. These clouds appear to be formed by a diurnal ascensional movement which is almost always observable. When the cloud is opposite the sun, the surfaces usually presented to the observer have a greater brilliance than the margins of the protuberances.
Page 50 - Aurora. — A luminous phenomenon due to electrical discharges in the atmosphere; probably confined to the tenuous air of high altitudes. It is most commonly seen in sub-Arctic and sub-Antarctic latitudes. Called aurora borealis or aurora australis, according to the hemisphere in which it occurs. Observations with the spectroscope seem to indicate that a faint "permanent aurora" is a normal feaBack 105 Cold wave ture of the sky in all parts of the world.
Page 58 - Sleet. — -1. Frozen or partly frozen rain; frozen raindrops in the form of particles of clear ice. (The official definition of the United States Weather Bureau.) 2. Snow and rain falling together.
Page 32 - This reading is kept in mind, the psychrpmeter immediately whirled again and a second reading taken. This is repeated three or four times, or more if necessary, until at least two successive readings of the wet bulb are found to agree very closely, thereby showing that it has reached its lowest temperature.
Page 36 - Bather large globular masses, white or grayish, partially shaded, arranged in groups or lines, and often so closely packed that their edges appear confused.
Page 32 - ... around the bottom of the bulb, just• where it begins to round off. As this knot is drawn tighter and tighter the thread slips off the rounded end of the bulb and neatly stretches the muslin covering with it, at the same time securing the latter at the bottom. To make an observation, the so-called wet bulb is thoroughly saturated with water by dipping it into a small cup or widemouthed bottle.
Page 37 - STRATUS (ST.). — A uniform layer of cloud resembling a fog but not resting on the ground. When this sheet is broken up into irregular shreds in a wind, or by the summits of mountains, it may be distinguished by the name Fracto-stratus (Fr.-St.) . NOTE.
Page 36 - ... at and near the surface, and commonly itself extends quite to the surface, at least during the stage of its development. In short, fog consists of water droplets or ice spicules condensed from and floating in the air near the surface; cloud, of water droplets or ice spicules condensed from and floating in the air well above the surface. Fog is a cloud on the earth ; cloud a fog in the sky.
Page 32 - THE WET BULB. — It is important that the muslin covering for the wet bulb be kept in good condition. The evaporation of the water from the muslin always leaves in its meshes a small quantity of solid material, which sooner or later somewhat stiffens the muslin so that it does not readily take up water. This will be the case if the muslin does not readily become wet after being dipped in water. On this account it is desirable to use as pure water as possible, and also to renew the muslin from time...
Page 54 - Insolation. Solar radiation, as received by the earth or other planets; also, the rate of delivery of the same, per unit of horizontal surface. Instability. A state in which the vertical distribution of temperature is such that an air particle, if given either an upward or a downward impulse, will tend to move away with increasing speed from its original level.

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