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 300 MAYER found. The river Mayenne traverses the de- partment from N. to S., joins the Sarthe near Angers, department of Maine-et-Loire, taking the name of Maine, and 7 m. beyond falls into the Loire, after a course of 120 m. It is navi- gable from Laval, about 65 m. The climate is mild and healthful. The soil, except in the S. districts, is not fertile. The chief manufac- tures are linen, canvas, cotton, and paper. It is divided into the arrondissements of Chateau- Gontier, Laval, and Mayenne. Capital, Laval. MAYER, Alfred Marshall, an American physi- cist, nephew of Brantz Mayer, born in Balti- more, Md., Nov. 13, 1836. He was educated at St. Mary's college, Baltimore. He has oc- cupied the chair of physics, with chemistry or astronomy, in several institutions, as follows : University of Maryland, 1856-'8; Westminster college, Missouri, 1859-'61 ; Pennsylvania col- lege, Gettysburg, 1865-'7; Lehigh university, Pennsylvania, 1867-'70; Stevens institute of technology, Hoboken, N. J., since 1871. In 1863-'4 he studied in the university of Paris. At Lehigh university he superintended the erection of an observatory, from which he made a series of observations of Jupiter. He was in charge of the party sent to observe the eclipse of the sun at Burlington, Iowa, Aug. 7, 1869, and took 41 perfect photographs of the eclipse. At Hoboken he began his researches in acoustics, in which he has made his most important discoveries; among these are: the measurement of the relative intensities of sounds of the same pitch ; an acoustic pyrom- eter ; the connection of the pitch of a sound with the duration of its residual sensation; the reflection of sound from flames and heat- ed gases; that the fibrils of the antennae of the mosquito are its auditory organs; the mechanism of hearing in mammals ; and new methods of sonorous analysis. In 1873 he was one of the editors of the "American Journal of Science and Arts," from which he withdrew on account of weakness of sight, and visited England. Among his numerous scien- tific papers are: "Estimation of the Weights of very small Portions of Matter" (1858); "Lecture Notes on Physics" (1868); "Re- searches in Electro-magnetism" (1870 and 1873); "An Investigation of the Composite Nature of the Electric Discharge " (1874) ; and Researches in Acoustics " (7 papers, 1871-'4). MAYER, Brantz, an American author, born in Baltimore, Sept. 27, 1809. His father was a merchant of German birth, engaged in trade with the East Indies and Mexico, and for many years consul general of Wtirtemberg in the United States. After graduating at St. Mary's college, Baltimore, he sailed for the East, vis- iting Java, Sumatra, and China, and returned in 1828. He practised law from 1832 till 1841, when he was appointed secretary of legation to .Mexico, where ho remained a year, and on his return edited for a short time the ' Haltimore American" newspaper. In 1807 he was appointed a paymaster in the Uni- ted States army, a post which he still held in 1874. Among his works are: "Mexico as it was and as it is" (1844; 3d ed., 1847); " History of the War between Mexico and the United States" (1848); "Mexico, Aztec, Span- ish, and Republican" (1852); " Calvert and Penn, or the Growth of Civil and Religious Liberty in the United States" (1852) ; "Cap- tain Canot, or Twenty Years in an African Slaver " (1854) ; " Observations on Mexican History and Archaeology," in "Smithsonian Contributions" (1857); "Mexican Antiqui- ties" (1858); and "Baltimore as it was and as it is" (1871). He has also contributed to the Maryland historical society the " Journal of Charles Carroll of Carrollton during his Mission to Canada," and " Tah-gah-jute, or Logan and Captain Michael Cresap." MAYER, Johann Tobias, a German mathema- tician, born at Marbach, Wtirtemberg, Feb. 17, 1723, died in Gottingen, Feb. 20, 1762. He gained a living when a mere youth by teaching mathematics. He early made himself known by scientific productions. The university of Gottingen in 1750 chose him its professor of mathematics, and appointed him director of its observatory. His "Zodiacal Catalogue," comprising 998 stars, is of high authority; and his "Lunar Tables," published in 1755, were deemed of such value by the English astronomer royal that the British parliament awarded his widow 3,000. The most im- portant of his discoveries was the principle of the " repeating circle," employed by Borda in measuring the arc of the meridian. MAYER, Julius Robert, a German physicist, born in Heilbronn, Wurtemberg, Nov. 25, 1814. He received his early education in the gymnasium of Heilbronn, and studied medi- cine at Tubingen, finishing his course in Mu- nich and Paris. In 1840 he made a voyage to Java, and spent the summer of that year in Batavia. While there he observed that the venous blood of some of his patients had a singularly bright red color, and he came to the conclusion that it was due to the fact that a less amount of oxidation sufficed to keep up the temperature of the body in a hot climate than in a cold one. The darkness of the ve- nous blood he regarded as the visible sign of the energy of the oxidatipn. His attention was drawn by this observation to the whole question of animal heat. One great principle of the physiological theory of combustion, he observes, 'is that under all circumstances the same amount of fuel yields by its perfect com- bustion the same amount of heat ; that this law holds good for vital processes ; and that hence the living body is incompetent to gener- ate heat out of nothing. We are thus driven to the conclusion that it is the total heat gener- ated within and without that is to be regarded as the true calorific effect of the matter oxi- dized in the body. From this again he in- ferred that the heat generated externally must stand in a fixed relation to the work expended