man and also as author of several books—an Autobiography (1854), The Humbugs of the World (1865), Struggles and Triumphs (1869) and Money-getting (1883). He died at Bridgeport, Connecticut, April 7, 1891.
Baro'da, a city of Hindostan. It is 250 miles north of Bombay, with which it is connected by railroad. It is the residence of the Gaikwar, a Mahratta prince. It has several Hindu palaces and temples and the court of the state to which it belongs. Its trade is considerable. Baroda is also one of the feudatory or native states in British India (area 8,099 square miles, with a population of 1,972,600). Population of the city, 103,790.
Barom'eter, an instrument for measuring the pressure exerted by the earth's atmosphere. It consists simply of a U-tube, one end of which opens into the earth's atmosphere, the other into a vacuum, the intermediate portion of the tube being filled with a liquid, usually mercury.
To clearly understand the barometer, we must recall that at the beginning of the 17th century the two following facts were supposed to be entirely independent, namely, (i) the fact that " nature abhors a vacuum" and (2) the fact that the air has weight. It was Torricelli (born in 1608, died in 1647), wno first showed that "nature abhors a vacuum because the air has weight."
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(l) MERCURIAL BAROMETER.
He illustrated this by taking a tube, more than 76 centimeters long and closed at one end, which he filled with mercury, as indicated in the figure. Placing his finger over the open end, he inverted the tube in a dish of mercury. The column of mercury fell a short distance, but remained standing in the tube approximately at the height of 76 centimeters above the surface of the mercury in the dish.
Torricelli thus showed that the weight of the earth's atmosphere is approximately that of an ocean of mercury covering the entire earth to the depth of 76 centimeters. But if this be the fact of the case, Torricelli argued that the height of the mercury in the inverted tube should diminish as one ascends in the earth's atmosphere. This test was shortly made by Pascal, who carried the inverted tube to the top of a mountain in France, and found that the mercury fell some seven or eight centimeters in the ascent. Such a dish of mercury and inverted tube is called a mercurial barometer. The vertical distance between the two surfaces of mercury, one in the tube, the other in the dish, is called the height of the barometer or, sometimes, the reading of the barometer. Ordinary barometers are furnished with graduated scales by which this height can be easily read.
In general the height of a barometer depends upon two factors: (i) the height of the atmosphere and (2) the average density of the atmosphere. Anything which changes either one of these will change the reading of the barometer.
Water vapor, when under the same pressure as air, has a density which is less than that of air. If then there be much water vapor in any portion of the earth's atmosphere, its density will be diminished and the mercury column which it supports will become shorter. The barometer is said to fall. But the same thing happens when the height of the atmosphere is changed or when its pressure is altered by cyclonic motion. The barometer is not, therefore, an instrument for telling whether or not it is about to rain; but for measuring the pressure of the earth's atmosphere. The readings of the barometer are, however, exceedingly useful, as one factor, in predicting the weather.
(2) ANEROID BAROMETER.
Since the mercurial barometer is not easily portable, geologists and travelers generally use a smaller form based upon the same principle as the ordinary steam gauge. It consists essentially of a hollow cylinder made of thin sheet-metal and bent into a circular form. After the air has «been partially removed from this cylinder it is hermetically sealed. As the pressure of the air outside diminishes, the metallic vessel tends to uncoil from the circular into a straight form. By a system of levers this motion is communicated to an index moving over a dial from which the barometric height can be read. Such an instrument is called an aneroid barometer. This is not nearly so reliable as the mercurial barometer; but when it is used with care and frequently compared with a mercurial barometer, it is exceedingly convenient for measuring altitudes. Hough, Hipp and others hav<2 invented excellent self-registering barometers.
Baudin of Paris makes a delicate thermometer which by changes of boiling-point of water will indicate differences of altitude as small as 30 feet. Such an instrument is equivalent to a barometer and is called a hypsometer,
Barr, Amelia Edith (Huddleston), Anglo-American novelist, was born at Ulw-r-ston, Lancashire, England, March 29, 1851, and was educated at the High School ai
TORRICELLl'S EXPERIMENT
