Page:The New International Encyclopædia 1st ed. v. 02.djvu/611

BARODA. which dominates the town. There are several fine European buildings, including the Anglican Church, dating from 1824, the Baroda College, the Anglo-Vernacular School, the Baroda State Library, and the Dufferin Hospital. The town has a splendid modern system of water-works since 1892, supplied from a distance of 18 miles by the artificial lake covering 4.71 square miles. Baroda is the residence of the Gaikwar, a protected Mahratta prince, who, in 1881, replaced Malhar Rao, the preceding ruler, accused of misrule from 1873-75. and suspected of an attempt to poison the British Resident. The State has been tributary to Great Britain since 1802. Population of town, in 1891, 116,400; in 1901, 103,800. These figures include a military cantonment of 5000 troops. Area of State, 8100 square miles. Population, in 1891, 2,415,400; in 1901, 1,953,000.

BAROM'ETER (Gk. βάρος, baros, weight + μέτρον, metron, measure). An instrument for measuring the elastic pressure of the atmosphere which is sometimes, but erroneously, called its weight. Plato and Aristotle maintained that the atmosphere has weight; Galileo and Torricelli knew that pressing upon the water in a well forced a portion of it to rise up the bore of a pump as fast as the piston rose. The fact that water could not be made to rise more than 33 feet in this manner showed to Galileo's mind the limiting pressure of the atmosphere — namely, about 15 pounds to the square inch.

Fig. 1. — Torricelli's Experiment. Fig. 2. — Ordinary Household Barometer. Fig. 3. — Siphon Barometer. Fig. 4. — Fortin Barometer. Fig. 5. — Section of Cistern of Standard Barometer. (Green Pattern.)

In 1643 his pupil and successor, Torricelli, desiring to find a convenient method of measuring the variations of atmospheric pressure, asked Viviani to use a short glass tube closed at one end, filled with mercury, and inverted in a basin of that heavy liquid, as in Fig. 1. As he predicted, so it was found that a column of mercury 30 inches high, corresponding to the atmospheric pressure (15 pounds to the square inch), was held up by the air-pressure and the upper portion of the glass tube was empty. This vacant space was called the Torricellian Vacuum. According to Hellmann, this simple apparatus was first called a barometer by Boyle. With the modifications and auxiliary apparatus necessary to secure the accuracy in measurement demanded by modern science, the mercurial barometer is now considered the standard instrument for measuring the elastic pressure of gases. In the normal barometers constructed for the International Bureau of Weights and Measures, maintained at Paris by the contributions of all nations for the purpose of securing accuracy and uniformity in all measurements, provision is made for measuring the temperature of the top and bottom of the mercurial column, the temperature of the metallic measuring-scale, the imperfection of tho vacuum, if any, the capillary effect at the surface of the mercury in the basin and in the tube, the verticality of the measuring-scale, the errors of pointing and reading, the exact density of the mercury, and every other source of error that has is supposed that with all these precautions the height of the column of mercury supported by the atmospheric pressure may be determined within the one-thousandth part of an inch, or the thirty-thousandth part of the whole pressure; but of course this accuracy is not obtained in the instruments ordinarily used in physical laboratories and meteorological observatories. Among the important forms of the mercurial barometer may be mentioned the siphon barometer illustrated in Fig. 3. If the diameter of the tube is perfectly uniform, the capillary effects at the upper and lower ends of the column partially neutralize each other, but not entirely so, because the mercury in the lower end is exposed to