Page:The American Cyclopædia (1879) Volume XI.djvu/79

 MALTHA MALTHUS 71 of history in several colleges, he devoted himself especially to geographical studies. He is secretary of the geographical society, and principal editor of the Nouvelles Annales des Voyages, and has published numerous works re- lating to geography. Among these are : Jeunes wyageurs en France (1840) ; Destinee de Sir John Franklin devoilee (1860) ; Nouvelles ac- quisitions des Busses dans VAsie orientale (1861); Les Etats-Unis et le Mexique (1862) ; Coup d'ceil sur le Yucatan, and Sonora et ses mines (1864); Canal interoceanique du Da- rien (1865) ; Histoire de Marcoussis (1867) ; and Histoire geograpMque et statistique de VAllemagne (4to, 1866-'8). He has also issued a revised edition of his father's geography (8 vols., 1852-'5), and, in conjunction with others, France illustree (3 vols., 1855-'7). MALTHA (Gr. fidWa, soft wax ; also denoting a mixture of wax and pitch, used for the sur- face of writing tablets, and for some kinds of cement). Pliny describes under this name an inflammable mud flowing from a pool at Samo- sata, on the Euphrates, which he says was simi- lar in nature to naphtha ; and this use of the word has led to its later application to viscid bitumens. It is the proper name for mineral tar, or all bitumens having the consistence of tar, and holding water and air in mechanical admixture in consequence of their viscidity. It occurs on the surface of the ground and issuing from springs, often accompanied by water, in various parts of the world, but most frequently in localities noted for the production of petro- leum, for which substance maltha is frequently mistaken. It appears to be a product of the partial oxidation or decomposition of certain unstable varieties of petroleum, and doubtless in 'all cases has a common origin with it (see PETROLEUM), as it passes by insensible degrees into petroleum on the one hand and asphal- tum on the other. It is found in this country throughout the length of California, in Texas, and at various places in the southwest, on both flanks of the Rocky mountains, and in Alaska. Among foreign localities may be mentioned Enniskillen in Canada, the islands of Barba- does and Trinidad, many localities in South America, some of the islands of the Grecian archipelago, and the Caucasus. In California, where there are immense quantities of this material, it occurs in every variety of density, from 0-94 to 1. In consistence it varies from that of a thin sirup to that of soft mortar. It issues there from a stratum of shale of consid- erable thickness which occurs in the miocene sandstones of the Coast range. It oozes from springs upon hillsides, over which it trickles ; it accompanies water in pools, and flows upon the surface of streams. It has been obtained from artesian borings at a depth of more than 450 ft. of the consistence of tar, and at a depth of 117 ft. so tenacious as to prevent the drill from penetrating further. In a few localities in this region the maltha is mixed with sand, the mixture forming strata or beds of great extent. At Enniskillen the maltha forms what are known as " gum beds." Barbadoes tar was long an article of commerce, used in medicine as a liniment. The California malthas have been used to some extent as a crude material for the manufacture of kerosene; but they have not been found to possess much value for this purpose when treated in the same appara- tus as is used for petroleum ; when it is distilled under pressure, or " cracked," a better result is obtained both as regards yield and quality. Little is known regarding the chemical consti- tution of maltha; but it is without doubt a mixture of hydrocarbons more dense than those found in petroleum. Some specimens contain nitrogen, as is proved by the fact that maggots are developed in immense numbers in pools of this substance. It is also possible that oxygen is a constituent of some varieties. While this substance is widely distributed and occurs in vast quantities in some localities, it is at present very much less valuable than petroleum. It is readily distinguished from it by its greater viscidity and its tendency to froth when heated, the froth often occupying 20 times the bulk of the maltha at the temperature of boiling water. MALTHUS, Thomas Robert, an English political economist, born at Albury, Surrey, in 1766, died in Bath, Dec. 29, 1834. His father was a gentleman of fortune, interested in classical and philosophical studies, and so intimate a friend of Rousseau that he was appointed one of his executors ; and David Hume was like- wise among his friends. In 1784 he was ad- mitted to Jesus college, Cambridge, and became one of the first classical scholars. He received his master's degree and a fellowship in 1797, entered holy orders, and divided his time be- tween the care of a small parish in Surrey and his studies in Cambridge. In 1798 he published anonymously the first edition of his work on population, which was subsequently much en- larged and modified. The title of the sixth and last revision (1826) is : "An Essay on the Prin- ciple of Population, or a View of its past and present Effects on Human Happiness, with an Inquiry into our Prospects respecting the future Removal or Mitigation of the Evils which it oc- casions." His object at first was to refute the theories of Condorcet and Godwin on human perfectibility and political optimism, by show- ing the necessary sufferings of the poor from the tendency of population to increase faster than the means of subsistence. The condition of the poor became the prominent feature of the sub- sequent editions. In 1799 he visited Sweden, Norway, Finland, and Russia, collecting, facts and documents in illustration of his subject; and during the interval of peace in 1802 he explored France and Switzerland. He married in 1805, and was appointed professor of history and political economy in the East India college at Haileybury, which post he held till his death. His other principal writings are: "Observa- tions on the Effects of the Corn Laws " (3d ed., 1815) ; " An Inquiry into the Nature and Pro-