built into the case and permanently connected with the coils. Such a galvanometer is often used in connection with a set of resistances for making measurements of resistance by the Wheatstone bridge (q.v.), and in that case the apparatus is known as a combination or portable testing set.
The D'Arsonval Galvanometer is quite different in its underlying principle from the instruments already described, for instead of having the magnet suspended and deflected under the influence of the current in a surrounding coil of wire, the coil itself is suspended between the poles of a compound horseshoe magnet. This coil is made of fine copper wire, wound on a rectangular frame of thin copper, and suspended by a fine wire of silver or copper, through which the current flows to the coil. The other end of the coil is connected to a similar wire, which leads to one of the binding posts, the supporting wire being connected with the other. The coil can thus oscillate freely in the space between the two magnets, and is in a strong magnetic field. When a current flows through the coil an opposing field is set up, and the coil, being free to move, is deflected. The motion of the coil can be determined either by a light pointer or by means of a mirror and a reflected beam, as in the case of the Thomson galvanometer. The D'Arsonval galvanometer is, perhaps, at the present time the most used of any form of galvanometer, since it is not affected by any external magnetic influences, and is easily adjusted. It is also aperiodic, or ‘dead beat,’ the coil coming to rest almost instantly and thus saving much time to the observer. For these and other reasons this galvanometer is extensively used for making tests and measurements, and certain modifications have been introduced, so as to render the apparatus portable and indicate current and electromotive force directly by means of a pointer and scale. These instruments form the most accurate ammeters and voltmeters.
Fig. 6. D'ARS0NVAL GALVANOMETER.
The Ballistic Galvanometer is intended to measure currents of extremely brief duration, such as those produced by the discharge of a condenser or by induction, and a magnetic needle is employed that has a period of vibration amounting often to several seconds. Instead of coming to rest after its deflection by the current, the needle will continue to oscillate, as there are no damping devices, and as the needle itself has considerable mass. When used to measure a momentary current, the deflection does not begin to move practically until the current has passed, and then the throw of the needle is noted. This instrument is used to determine the capacity of a condenser and to measure self-induction. Consult Kempe, Handbook of Electrical Testing (6th ed., London, 1900); Thompson, Elementary Lessons in Electricity and Magnetism (New York, 1901), contains a full elementary description of galvanometers and the theory of their action.
GAL′VESTON. A city, port of entry, and the county-seat of Galveston County, Tex., on Galveston Island, at the mouth of Galveston Bay, 50 miles southeast of Houston; on the Southern Pacific, the International and Great Northern, the Missouri, Kansas and Texas, the Gulf, Colorado and Santa Fe, and other railroads (Map: Texas, G 5). Regular steamship communication is maintained with important European, Mexican, and Cuban ports, and there are also lines to China, Japan, and South America, as well as several coastwise lines. The street-railway system comprises 35 miles of track.
The city, including Pelican Island, has a total area of nearly 13 square miles, and is built toward the inland side of the island, while along the outer side extends, for a distance of 30 miles, a hard and level beach. Galveston is the seat of Saint Mary's University (Roman Catholic), opened in 1854, and of the medical department of the State University. It has two Roman Catholic academies, the Ball High School (one of the city's principal buildings), and a fine library in course of erection, which is to be endowed with $400,000. There are two orphan asylums, a home for friendless children, and an old women's home, and two well-equipped hospitals, Saint Mary's and the John Sealy, the latter used in connection with the State Medical College. Other notable structures are the county court-house, custom-house and post-office, city hall, railroad depot. Young Men's Christian Association Building, Masonic Temple, and several of the business buildings. There are here three forts, a life-saving station, a State quarantine station, an office of the United States Marine Hospital Service, and the State branch of the United States Weather Bureau. A railroad bridge, two miles long, connects with the mainland.
Galveston, with an admirable location for a commercial centre, has also improved means for handling its important commerce. Both by rail and water transportation facilities are excellent. By means of rock jetties, 12 miles long, completed by the Federal Government in 1896 at a cost of $8,000,000, the channel between the island and the mainland has been deepened to afford an average of 27 feet. Terminal tracks, aggregating 50 miles, extend to the wharves, of which there are now 6 miles. There are four export grain elevators, with a total storage capacity of 3,750,000 bushels, and one clearing and conditioning elevator, a coal elevator, marine works, creosoting works, etc.
Galveston in 1901 ranked third among ports of the United States in exports (value, $106,526,508), a gain of $14,000,000 over 1900; and thirty-sixth in imports (value, $1,048,866). Since the improvements in the harbor, the export trade has substantially increased, though, on the contrary, imports have decreased. The city alternates with New Orleans as the largest cotton-exporting centre in the United States, is the first in the amount of cottonseed products, and eighth in wheat. In value the leading exports for 1901 were: Cotton, $85,857,145; oil cake and meal, $5,568,449; cottonseed oil, $1,502,307; wheat, $11,476,205; flour, $462,607; lumber, $479,457. The live-stock trade is now compara-
