that various dissimilar gases might exist, and pneumatic
chemistry was founded.Although the full value of this discovery was not immediately visible, it added so greatly to Black s reputa tion that iu 1756 he was chosen to succeed Dr Cullen as lecturer on chemistry in Glasgow University. He was also appointed to the chair of anatomy, but, not; finding- its duties congenial, exchanged it for the professorship of medicine. For some time he was so assiduous in preparing his lectures as to neglect fresh investigations, and even left the examination of carbonic acid, or fixed air, to be afterwards completed by Cavendish. He was highly esteemed as a professor by his students and colleagues, and became, through his attention and urbanity, a very popular physician in Glasgow. From 1759 to 1763 he prosecuted inquiries resulting in his theory of latent heat, which may be thus summarized A solid liquefies or a fluid vaporizes through heat uniting with the solid or fluid body, and a fluid solidifies or a gas liquefies through the loss of heat ; but in no case is this increase or diminution of heat detected by the senses or the ther mometer,- Black therefore named that heat latent which alters the condition, not the temperature, of a body. He likewise proved that bodies of equal masses require different increments of heat to raise them to the same sensible temperature a doctrine now known as the law of specific heat.
His theory of latent heat he corroborated by numerous experiments, but he never published a detailed account of it, m omission which enabled others to lay claim to his great discovery. Thus M. Deluc, in 1788, declared himself its author. In 1766 Black was elected to succeed Cullen in the chair of chemistry at Edinburgh University. In this office he bestowed great care on his lectures, striv ing to give a lucid exposition of ascertained facts rather than to effect new discoveries ; and such an interest did he communicate to his subject, that chemistry was for a time, it is said, regarded as a fashionable accomplishment iu the Scottish capital.
He was intimate with the great men who adorned Edin burgh society during the second half of the eighteenth century, counting among his friends "Watt, Hume, Robert son, Hutton, Adam Smith, and, at a later period, Robison. Playfair, and Dugald Stewart. His constitution had always been feeble, and he was ultimately reduced to the condition of a valetudinarian, which may account for the indifference he manifested during his latter years to original research. He retired from his professorship iu 1796, and ou the 26th November 1799 passed away so quietly that a cup of water, which he had held in his hand, remained unspilled after he had breathed his last. At the instance of Lavoisier he had been elected a member of the Paris Academy of Sciences.
Black was singularly modest, gentle, and sincere ; his philosophic tranquillity was seldom ruffled ; and his sagacious diffidence was equally conspicuous in his scien tific inquiries and in his social relations. He has been called the founder of modern chemistry. When he began his career that branch of knowledge had only recently been raised to the rank of a true science through the efforts of Hermann Boerhaave, and was in many quarters even regarded with suspicion as being akin to alchemy on the one hand, and to humble trades on the other. But after Black s discoveries its scope and capabilities were immensely extended, and no one could then question its claim to rank with the most important sciences. The only works of his which appeared in print during his life time were Experiments on Magnesia, <tc., Observations on the more ready Freezing of Water that has been boiled, and Analysis of the Waters of some Boiling Springs in Iceland. His lectures ou chemistry were issued after his death. (Of. Prof. Robison s Life of Black.)
BLACK FOREST (German, Schwarzwald), an exten sive upland district on the right bank of the upper Rhine, stretching from that river to the Neckar and upper Danube. See Baden and Würtemberg.
BLACK SEA, or Euxine, the Pontus Euxmus of the ancients, is a large inland sea, bounded on the W. by the Turkish provinces of Rumilia, Bulgaria, and Moldavia ; on the U. by South Russia, including Bessarabia, Kherson, and Taurida ; on the E. by the Russian provinces of Circassia and Transcaucasia ; and on the S. by the Turkish provinces of Asia Minor. It is entered from the Mediterranean through the channel of the Dardanelles or Hellespontus, the Sea of Marmora or Propontis, and the channel of Constantinople or Thracian osphorus; and it is connected with the Sea of Azoff, or Palm Ma-otis, by the strait between the Crimea and the isle of Taman, anciently the Cimmerian Bosphorm, and known by the various modern names of the Strait of Kertch, of Yenikale, and of Taman.
The first navigators of Greece who ventured into this sea having been repulsed or massacred by some of the fierce tribes inhabiting its coasts, their countrymen gave it the name of Pontus Axenos, or "sea unfriendly to strangers." But when the repeated visits of the Greeks had rendered these tribes more familiar with strangers, and commercial intercourse had softened down the original ferocity of their character, Grecian colonies were established at different points on the shores of this sea, and the epithet Axenus was changed into Euximis, which has the opposite import, and means "friendly to strangers." The modern name seems to have been given to it by the Turks, who, being accustomed to the navigation of the ^Egean, the islands of which furnish numerous harbours of refuge, were appalled by the dangers of a far wider expanse of water without any shelter, subject to sudden and violent storms, and often covered with dense fogs.
its long diameter lying nearly E. and "W. Its greatest length, from the head of the Bay of Burghaz in Rumilia on the west to the boundary between Transcaucasia and Asiatic Turkey near Batum on the east, is about 720 miles. Its greatest breadth is in its western portion, between the estuary of the Dnieper on the north and the mouth of the Sakaria on the south, where it is 380 miles; its middle portion is narrowed, by the projection of the Crimean peninsula on the north and of the coast line of Anatolia between Cape Kerempe and Sinope on the south, to 160 miles ; but further east it widens out again between the Strait of Kertch on the north and the mouth of the Kizil Irmak (the ancient Halys) on the south, to 260 miles. Its total area, including the Sea of Azoff, is about 172,500 square miles. The western coast line of the Black Sea, for some distance northwards from the Bosphorus, is high and rocky, having ranges of hills at its back; and the water rapidly deepens to from 30 to 40 fathoms. Between their northern extremity and the range of the Balkans (the ancient Hcemus), which extends east and west, terminating in Cape Emineh, there is a large bay, named after the town of Burghaz at the head of it, which affords a safe anchorage for large ships, the only one on this coast. Be tween Cape Emineh and Varna the coast line is again low and the shore shallow ; and the same condition extends, with but little interruption, along the low-lying region called the Dobrudscha, which extends to the mouth of the Danube. This great river discharges itself by seven mouths, among swampy islands and shifting banks ; and the quan tity of detritus brought down by it is so large as not only
to form a very extensive bar, but also to require the con-
