HERTZ
870
HESTIA
attention to the then new science of photography. He was the first to use glass as a support for the sensitive film; and to him we owe the terms "positive" and "negative" as used in photography. He is buried in Westminster Abbey near the grave of Newton.
Hertz, Heinrich Rudolf, a brilliant German electrician, born at Hamburg, Feb. 22, 1857, died at Bonn, Jan. i, 1894. Having abandoned his early intention of being an engineer, he entered Berlin University in 1878. Helmholtz at once recognized the remarkable abilities which he displayed in the line of physics, and immediately assigned him the problem of finding to what extent electricity exhibited inertia. The solution which Hertz found for this problem (1880) is his first important piece of work. In 1880 he was appointed assistant in the physical laboratory at Berlin. In 1885 he accepted the chair of physics in the engineering school at Carls-ruhe. It was in this laboratory, in 1888, that he completed his immortal work on the connection between light and electricity. Maxwell, interpreting Faraday, had prophesied on purely mathematical grounds that electrical forces are propagated through space according to the same laws and the same speed as light. To prove or disprove by experiment this prediction of Maxwell's was suggested by Helmholtz as a prize question for the Berlin Academy of Sciences. This is the problem which Hertz solved in • 1888, thereby confirming Maxwell's views and making it highly probable that light is nothing but electricity in vibration. While at Carlsruhe, he married Miss Elizabeth Doll, a daughter of one of his colleagues. In the spring of 1889 he received a call from the University of Bonn, which he accepted. Here he remained until his too early death. The last monument of his genius is his Principles of Mechanics, a volume upon which he worked during the last three years of his life and which was published posthumously. This profound work is understood by very few people. See also his Electric Waves and Miscellaneous Papers, both of which have been translated into English. The best account of his genial and lovable character is to' be found in the prefaces and introductions to his works, partly by Helmholtz and partly made up of Hertz's letters to his family.
Her'vey Islands. See COOK ISLANDS.
Hesiod (he'si-ud), one of the earliest Greek didactic poets, was born at Ascra at the foot of Mt. Helicon. His era is that of 735 B. C. or so. He wrote Works and Days and the Theogony.
Hesperides (hes-perfi-dez), the name of the sisters who guarded the golden apples given by Gsea to Hera upon her marriage with Zeus. Their genealogy and number are a matter of dispute. The gardens of
the Hesperides were thought to be in the far west, on the shore of the ocean. The apples were stolen by Hercules and restored by Athena.
Hesse {hesr), or Hesse=Darmstadt, a grand duchy of the German empire. It is separated into two division by a strip of Hesse-Nassau. The principal rivers are the Rhine, which divides two of its provinces, the Main and the Neckar. Mainz (91,124), Worms (43,841), Offenbach (59,806) and the capital, Darmstadt (83,385) are the principal cities. There are a university at Giessen and one at Darmstadt. Hesse yields iron, manganese ore and peat, and its industries are mainly the making of leather boots, fine upholstery, tobacco, cigars, chemicals etc. Its total population is 1,282,219. It was founded by an ancient German tribe, and governed independently until acquired by Prussia. Ancient Hesse was divided in 1567 among the four sons of the landgrave, Philip, and in 1604 two of the branches became extinct, and it was formed into Hesse-Cassel and Hesse-Darmstadt. Its area, including Upper and Rhenish Hesse and Starkenburg, is close upon 3,000 square miles.
Hes'sian Fly a two-winged insect associated in a family with gall-gnats, wheat
midge etc. These are minute insects, but their larvae have caused more extensive damage to the wheat crop than any other insect. The eggs hatch into a very small flattened maggot of a
pale red color; these crawl into a joint, near the base of the wheat-stem, just where a leaf fits into the stalk, burrow into the stem, and sap its life and vigor. They pass into a pupa-stage and are known as flax-seeds. There are two or three broods a year. This fly received its name from the belief that they were brought to the United States by the Hessian troops during the War of the Revolution. It has been active ever skice Revolutionary days, but some years have been years of especial disaster, as 1789, 1817, 1846, 1863, 187^3, 1876 and some succeeding periods. It is combated by burning the stubble of wheat-fields, as the pupa lives over winter . See Third Report, U. S. Entomological Commission 1880-82.
Hes'tia, the Greek goddess of the heartlj and home. Hestia was the oldest daughtei of Cronos and Rhea, and, having beer
HESSIAN FLY
