of Virginia. Transferred to the army of the Potomac, he followed it through the campaign of 1864, having charge of all the wounded, and establishing and moving the hospitals as circumstances required. The number of patients thus under his charge from May, 1864, to March, 1865, was more than 100,000. From the latter date he was medical director of the 9th army corps until the close of the war, when "for faithful and meritorious services" he received the rank of colonel of volunteers by brevet. From March, 1866, to January, 1869, he was sanitary superintendent of the New York board of health. He visited California three years later, for the improvement of his health, and died there. His published works are: a treatise on "The Disorder known as Bronzed Skin, or Disease of the Supra-Renal Capsules ("New York Journal of Medicine," May, 1860); "Reports of the Sanitary Superintendent of the Metropolitan Board of Health " for 1866, 1867, and 1868; and an article on "The Metropolitan Board of Health" ("North American Review," April, 1868).

DALTON, John, an English chemist, author of the atomic theory, and of that of the constitution of mixed gases, born at Eaglesfield, near Cockermouth, in Cumberland, Sept. 5, 1766, died in Manchester, July 27, 1844. With his parents, he belonged to the society of Friends. He received his first instruction at the school of his native village, and in 1781 became usher in a school at Kendal, where he remained till 1793, when he was appointed professor of mathematics and natural philosophy in the New college at Manchester, which was removed to York in 1799. He continued his lessons in private schools for years, occasionally giving lectures on the physical and experimental sciences in neighboring towns and cities. In 1788 he began a series of important meteorological observations, and in 1793 published his first separate work, entitled "Meteorological Observations and Essays." This was one This was one of his favorite pursuits, and he continued to collect and record meteorological observations until his death. In 1794 he gave an account of a singular defect in his own vision which rendered him incapable of distinguishing certain colors; green, red, purple, and blue, all appearing alike to him. He supposed this peculiarity to be due to the color of the retina or of the fluids of the eye; but after his death no abnormal coloration was discovered on dissection. This defect of vision, which is not very uncommon, has sometimes been called Daltonism since the publication of his paper. (See COLOR-BLINDNESS.) He wrote numerous articles for the "Gentleman's and Lady's "Gentleman's and Lady's Diary," the "Memoirs of the Manchester Society," "Nicholson's Journal," the "Philo"the "Philosophical Magazine," and the "Transactions of the Royal Society of London." In 1801 he published "Elements of English Grammar." În 1802 he wrote six dissertations for the Memoirs of the Manchester Society," in one

of which he unfolded his celebrated theory of the "Constitution of Mixed Gases." The leading feature of this theory is that gases which do not form new chemical compounds act on each other as a vacuum, diffusing themselves among each other by their own elasticity. The greater part of Dalton's experiments were made to ascertain the influence of heat in the production of physical and chemical phenomena; and much of the progress of modern science in this department is due to his researches. Other subjects treated in these papers were "The Force of Vapor of Water and other Fluids at Different Temperatures in the Torricellian Vacuum, and other Atmospheric Pressure," and "The Theory of Evaporation and the Expansion of Gases by Heat." These writings display profound reasoning based on accurate observations, and have rendered great service to pneumatic chemistry and modern investigations on the specific gravity of gases. His celebrity, however, rests mainly on his atomic theory, which he began to work out in 1803, and explained in lectures in 1804. This theory was fully propounded in his "New System of Chemical Philosophy," the first volume of which appeared in 1807, and the second in 1810, followed by a third in 1827. (See ATOMIC THEORY.) In his papers on subjects connected with meteorology, he has left valuable remarks on evaporation, rain, the aurora borealis, winds, and dew. His observations on the latter contain the principles of Dr. Wells's theory of dew, and of Daniell's hygrometer. In 1821 he was elected fellow of the royal society, and in 1826 received a gold medal from that society for discoveries in science. In 1822 he visited France, where he was received with much distinction. In the reign of William IV. the English government gave him a pension of £150 a year, which was subsequently increased to £300.

He

DALTON, John Call, an American physiologist, born at Chelmsford, Mass., Feb. 2, 1825. graduated in arts at Harvard college in 1844, and in medicine in 1847. He first attracted attention as an original physiological writer by an essay on the corpus luteum, which received the annual prize offered by the American medical association in 1851, and he was appointed professor of physiology in the medical department of the university of Buffalo, where he inaugurated in this country the teaching of physiology with illustrations by vivisection. He resigned this professorship in 1854, and occupied the chair of physiology in the Vermont medical college from 1854 to 1857, and in the Long Island College hospital from 1859 to 1861. In 1854-5 he gave a course of lectures on physiology in the college of physicians and surgeons in New York, in place of Prof. Alonzo Clark. In 1855 he was appointed to that chair, which he has since filled. His contributions to the literature of physiology have been numerous since 1851. He has published several important articles in the "American Journal of the

secondary one of supplying it with water, is one of the remarkable pieces of civil engineering of the day. The dam is 164 ft. high, and between the extreme ends at the top, where it is anchored in the rock, the distance is 100 metres or 328 ft. The adjoining diagram, fig. 1, shows a horizontal ground section of the foundation, and also that of the curved upper edge, which is an are whose chord is 100 metres, and its versed sine 5 metres. The facings of both sides are curved surfaces, calculated as near as

possible to allow that RESEV

breadth of structure

which at every point

FIG. 1.-Dam across the Furens,

would bear a constant proportion to the strain given by the forces exerted against it. The soil upon which the dam is built is mica schist, and the structure is sunk into the rock at the bottom and sides. In both the excavation was continued until perfectly solid rock was reached. The wall is built of solid masonry, the stone being carefully selected, and not placed in tiers, but so joined as to produce the effect of a monolith, and, with the exception of a small portion at each end, was laid in hydraulic cement. The work was begun in 1858, but it was not till 1865 that it could be tested by a great depth of water. In December of that year the Furens was greatly swollen, and the reservoir was filled to the height of 46 metres, and in the following March to the height of 47 metres. The pressure produced no movement of mass, or escape of water, except a dampness owing to its being forced through the pores of the material by the enormous pressure, which at the depth of 47 metres or 154 ft. was more than 67 lbs. to the square inch, or about 4 tons to the square foot.-A COFFER DAM is a barrier erected to exclude water from an enclosure, usually for the purpose of allowing excavations to be made. It may be construct

推推

FIG. 2.-Coffer Dam.

ed in a variety of ways, and of different materials, depending on the size of the work, the depth of the water, and the material of which the bottom is composed. If it is of clay or

similar substance, piles may be driven about the enclosure, in two, three, or four rows, and the intervening spaces filled with gravel and clay. Between the piles of the inner row clay, or if necessary hydraulic cement, may be used, after which the water may be pumped out. (See fig. 2.) If the bottom is of quicksand, the construction of a coffer dam which will allow of much excavation is attended with great difficulty. Such was the case in building the dry dock for the Brooklyn navy yard; the exposure to water, however, was only on one side. For more than 60 ft. below the superstratum of black mud the bottom consisted of an impalpable micaceous sand, which, saturated with water under pressure, flowed like a mobile dense liquid. In this material a pit was to be excavated having an area of over two acres at the top and one at bottom, and a depth of 37 ft. below mean high water. Piles of yellow pine 40 ft. long and 15 in. square were driven in close contact around the outer end of the proposed excavation, the intervals between the rows being 10 or 12 ft. These were filled in with the sand excavated. The piles were held together with oak wales and two-inch tie bolts. This barrier was forced inward by a pressure of less than 10 ft. of water, and when the excavation reached 30 ft. the water came in under the piles and filled the pit. A new and stronger dam was then commenced, and piles from 10 to 15 ft. longer than the first were driven close together in two rows 30 ft. apart, outside of the old work, and the space between filled with gravel and coarse stone. A third row was driven within the old work from 12 to 15 ft. below the proposed level of the foundation, and the space behind filled in with gravel. This dam was retained in place during the progress of the excavation only by the closest attention, although the walls were over 60 ft. thick and contained six rows of piles of timber from a foot to a foot and a half in diameter. When the bottom will not admit of pile driving, a

frame of cribwork, lined with planking, made water-tight and loaded with stone, is sunk in position, and any crevices at the bottom are stopped with clay or hydraulic cement or concrete. If a shaft of only a few feet in diameter is required to be sunk into a rock for the purpose of excavating, a coffer dam may be constructed of an iron cylinder, which, having a strong flap of India-rubber sheeting around its bottom, may be made tight by means of weights. As the excavation proceeds, an inner cylinder may be slid down below the surface of the rock, like the slide of a telescope. It is, however, difficult to get and maintain such a piece of apparatus in position in a harbor where moderate waves are liable to be raised. Cribwork which may be weighted to any required degree and floated into position, and sunk by additional weight of stone, will generally be found more practicable. A combination of cribwork and iron cylinder in a coffer dam is represented in the article BLASTING.

These suburbs lead into the Meidan, another | suburb running S., which terminates in Bawabet Illah (the gate of God), through which the caravans pass on their way to Mecca. Damascus is regular and cleanly for an oriental city; its streets are long and narrow, and tolerably paved with basalt, and many of its residences, though mean and unattractive without, are magnificent within. Almost every house has a fountain more or less decorated in the middle of the court. The market places are well constructed and adorned with numerous pillars. There are many fine baths with marble pavements. The bazaars are numerous. Each class of merchants and artisans has its own bazaar, some of them being very extensive, as those of the goldsmiths, the druggists, the butchers, traders in cotton stuffs, pipe makers, &c. The great khan is a large

building filled with various commodities, and frequented by merchants from distant lands. Many of the khans are of great antiquity, and afford even in their present state a good idea of the manner in which business was conducted in ancient times. Besides the mosque Abd el-Malek, there are several others of much beauty, four Jewish synagogues, and Greek, Greek, Maronite, Syrian, and Armenian churches. The most numerous Christian communion is the Non-united Greek church, of which the third highest dignitary, the patriarch of Antioch, has since the 16th century resided in Damascus. It is also the seat of the United Greek (Melchite) patriarch, and of a United Syrian and of a Maronite archbishop. The first Protestant congregation has been organized by Presbyterian missionaries from America.-Damascus is the centre of the com

merce of Syria; and its trade is very much increased by its forming the meeting point of all the pilgrims to Mecca from the north of Asia. The number of pilgrims who make Damascus their place of rendezvous, with their attendants, amounts annually to several thousands. The city at such times presents the appearance of a vast fair, and every vacant place is filled with camels, horses, mules, and merchandise. Caravans proceed from Damascus also to Bagdad and Cairo. The principal imports by these various channels are broadcloths, different sorts of metals from the coasts of the Mediterranean, and shawls, muslins, and Indian stuffs, which are brought by way of England. Its own manufactures consist chiefly of silk and cotton fabrics, highly finished saddles and bridles, fine cabinet work, jewelry, gold and silver trimming, and excellent soap, made of olive oil, soda, and quicklime. Large quantities of dried

fruits and sweetmeats are exported to Constantinople. In former days Damascus was celebrated for the manufacture of sabres that would bend to the hilt without breaking, while the edge was so keen as to divide the firmest coat of mail. (See DAMASCUS BLADES.)—This very ancient city was built, according to some traditions, by Uz, the son of Aram; it is repeatedly mentioned in the history of Abraham. It was the residence of the kings of Syria during three centuries, and has experienced many and great changes in every period of its history. Hadad, who is called by Josephus the first of its kings, was conquered by David, king of Israel, but its subjection was of short duration. In the reign of Ahaz it was taken by Tiglath-pileser, who slew its last king Rezin, and added its provinces to the Assyrian empire. The capture of Damascus figures among the lately discovered Assyrian sculp