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* COMMENSALISM. 208 COMMERCE. vol. iii. (London, 1895) ; Semper, Animal Life (New York, 1881). For fishes as commensals, consult: .Jordan and Evermann, Fishes of Sorth and Middle America, pp. 924, 966 (Washing- ton. 1900) ; Harrington. "On Nereids Commensal with HennitCrabs;" Transaclions of Xeiv York Acadcnii/ of Srioiccfs, vol. xvi., 1897, p. 215. COMMENSURABLE (Lat. commensurahilis, from com-, together + mcnsurare, to measure, from mciixuru. measure, from metiri, to mete). Two magnitudes which are of the .same kind, and each of which contains a third magnitude an exact number of times, are said to be com- mensurable — e.g. a foot and a yard are com- mensurable, an inch or a foot being a common measure. The numbers 13 and 35 are commen- surable, each being divisilile by 5. ^Magnitudes which have iio common measure — that is, are not multiples of the same unit, however small that unit is taken, are said to be incommensurable — e.g. the side and diagonal of a square are incommensurable. The diameter and circumference of a circle are incommensur- able: 2 and l/2, Vo and Vl are incommen- surable. Numbers like V2, that are not com- mensurable with ordinary rational numbers, are also called incommensurable. In arithmetic, numbers prime to one another are sometimes called incommensurable, since they have no com- mon measure except the unit of counting, which, used as a multiplier or divisor, does not change the number affected. See JIultiple ; Ieeatioxal NUMRER. COMMENTARIES, C.esar'.s. The title of the two extant vorks of Julius C:i;sar, the account of the Gallic War {De Bello Galli<:o) and of the Civil War {De Bello Civ'U). The former is a concise narration of the author's campaigns in Gaul, published in B.C. 51. in seven books, to which an eighth book was added by Aulus Hirtius. The simple and untechnical language and the importance of the matter have made it the most generally known work in the Latin liter- ature. The memoirs of the Civil 'War were after- wards extended by other writers to embrace the Alexandrine, African, and Spanish wars. COMMENTRY, ko'm;i>''tre'. A town in the Department of Allier. France, eight miles southeast of Jlontlucon on the (Ei. It stands in the centre of one of the most important coal- fields of France, and since 1850 has risen from a mere village to a busy and populous to^vn, whose inhabitants are mostly engaged in the coal-mines and iron-works. There are, besides, manufac- tures of wood and mirrors. Population, in 1901, 11,169. COM'MER, Franz (1813-87). A German inu- sician. liorn at Cologne, in which city he studied music with Leidl and Klein. After holding a position as organist of the Carmelite church there, he went to Berlin in 1832 to study with A. W. Bach. A. B. Jlarx. and Rungenhagen. He was reyens chori at the Catholic Hedwigskirche; singing-teacher at numerous schools, and founder (with Kiister and KuUak). in 1844, of the Ber- lin Tonkiinstlerverein. He was, in addition, royal music director, a senator of the Berlin Akademie, and president of the (resellschaft fiir Musikforschung. He edited a nimiber of collec- tions of old music, and composed numerous masses, cantatas, and choruses. COMMERCE (Lat. commereium, commerce, intercliange. from com-, together -|- merx, mer- chandise, from Lat. merere, to gain, Gk. /t^pos, nuros, share). In its general aeee])tation, a term denoting international traffic in goods, or what constitutes the foreign trade of all countries as distinguished from domestic trade. The first for- eign merchants of whom we read, carrying goods and bags of silver from one region to another, were the Arabs, the reputed descendants of Ish- mael and Esau. Their trade was by land. The first maritime carriers of goods were the Pluenicians, who dwelt on a narrow strip of land on the east- ern shore of the Mediterranean, and were the founders of the great emporiums of Tyre and Sidon. The Phoenicians established an easier and securer passage between Eg}-pt and Syria than had before been loiown. The corn and wine of the Nile, and the oil, silk, dyes, and spices of western Asia flowed through their hands. From carriers they became merchants, and to merchandise they added manufactures. They traversed the shores of the Jlediter- ranean, established colonies in the Greek is- lands and foimded Carthage, one of the most noted commercial cities of the ancient world. The power of the Phoenicians disappeared with the rise of the Greek cities — Athens, Corinth — and of their colonies ; of Carthage, then in full fame: and of Alexandria, the great seaport founded by Alex.ander the Great. AA'hile Rome was giving laws and order to the half-civilized tribes of Italy, Carthage, operat- ing on a different base and by other methods, as opening trade with less accessible parts of J!lurope. The strength of Rome was in her le- gions, but that of Carthage in her ships : and her ships could reach realms where legions were powerless. Her mariners had passed the mys- terious Pillars of Hercules into the Atlantic, and established the port of Cadiz. They founded Carthagena and Barcelona, and had depots and traders on the shores of Gaul. This prosperity of their commerce led to wars with Rome, which ended in B.C. 146 with the destruction of Car- thage. In the same year the Romans captured and l)urned Corinth, which was then an important commercial city. In a.d. 273 land commerce suf- fered a disastrous blow, when Palmyra was in great part destroyed bj' the Romans. Growth of Comjiekce. The repeated inva- sions of Italy by the Goths and Huns gave rise to the founding, for defense and for trade, of the city of Venice, about the middle of the fifth cen- tury — a city that for more than a thousand years stood foremost in the trade of the world. The Venetians traded with Constantinople, Greece, Syria, Egypt. India, and Arabia, and their vessels carried the products of the East to the ports of w-estern Eurojje. They had posses- sions on the coast of Greece, and became rulers in the Ionian Islands and in Cyprus. Their rivals, the Genoese, planted colonies on the shores of the Hellespont and the Black Sea, the most flourishing of which was Kaffa (the modern Feodosia ) . in tlie Crimea, a great emporium of the commerce between Europe and Asia. A vast commerce was carried on in the Middle Ages by the tow-ns of the Hanseatic League, situated on the shores of the North Sea. and the Baltic, and the rivers flowing into them. When the chief objects of conunerce were the skilled products of the East, the South German cities — Nuremberg