Fatimite caliph, Al Moez, whose army had conquered Egypt in 969. It is said that the new city was originally the camp of Jauhar whilst besieging Fostat, which gradu ally grew into a town, and got the name of Al Kahirah ("Victrix"), whence our Cairo. In 1176 the city was attacked by the Franks ; and shortly afterwards it was fortified by Saladin. From 1507 to 1798 it remained the capital of the Turkish province of Egypt; but in the latter year it was captured by the French, who kept posses sion till they were driven out in 1801 by the Turkish and English forces. Mehemet AH secured his position by the massacre of the Mamelukes in the citadel in 1811, and
laid the basis of the present independence of Egypt.CAISSON, in engineering work, is a chamber of iron or wood which is used in the construction of subaqueous foundations, such as those required for the piers of bridges, &c. Its object is the same as that of a cotter-dam, viz., to allow the work to be carried on below the water- level, but it is used in places where either the water or the permeable soil is too deep to allow a dam to be erected. In cases where the bridge piers are hollow cylinders of iron, they not unfrequently form their own caissons, their own weight, or that of ballast placed upon them, forcing their lower edges into the ground. The material left within them is dredged up or excavated as they de scend. Where, however, the soil is not so soft, or is mixed with stones, this self-lowering becomes impossible. The lower part of the caisson is then commonly formed into an air chamber, open at the bottom, and resting upon the bed of the river Air is pumped into this at a pressure corresponding to its depth below the surface of the water, and the excavation is carried on by men working in the compressed air as in a large diving-bell. In some cases the masonry of the pier is built within the caisson on the top of the chamber as it descends, the chamber itself being eventually filled up with masonry or concrete, and left to form the permanent base of the structure ; in others the caisson is lowered (as the excavation goes on) by weights ; and when the required depth has been reached, the masonry is commenced within the air-chamber, and the whole caisson raised again as the building proceeds. Probably the largest caissons ever used are those of the East River Suspension Bridge (a structure still unfinished) at New York, of which one was 172 feet long by 102 feet wide. See Bridges. For military caissons see Fortification.
CAITHNESS, the most northern county of the Scottish mainland, bounded W. and S. by Sutherlandshire, and E. and N. by the Northern Ocean, is situated between 58 8 and 58 40 N. lat., 3 and 3 55 W. long., and has an extreme length of 53 miles, an extreme breadth of 33, a coast line of 105 miles, and an area of 455,708 acres or 712 square miles. The form of Caithness resembles an irregular triangle, having as its greatest side the line of coast on the S.E., stretching from the Ord of Caithness to Duncansby Head. The surface of the county generally is flat and tame, consisting for the most part of barren moors, and being almost entirely destitute of trees. It presents a gradual slope from the north and east upwards to the ridge of hills on the west and south, which separates it from Sutherlandshire, and on the southern boundary, where it is bifurcated, attains considerable elevation. The one branch, called the Maiden Paps, contains the peak of Morven, 2334 above the level of the sea ; the other, continuing in the line of the main ridge, juts into the sea, and terminates in the huge granitic precipice of the Ord. In the centre of the county, hemmed in by the hills on the western boundary, the ridge of the Maiden Paps, and the sea, is a large undulating plain comprising nearly four-fifths of the whole extent. On its southern side it is broken up by several detached hills, and in the interior contains a con siderable number of small lakes. The most depressed part of the county lies in the peninsula formed in the north east corner by the indentation of Dunnet Bay and Sinclair Bay. The more elevated portion presents a light sandy soil, which admits of considerable cultivation, but the low grounds are covered with extensive morasses, producing only heath and rough grass.
The geological formation consists chiefly of sandstone, sandstone flag, and occasionally limestone ; but granite and gneiss are also found in the west. On the east Caith ness presents a precipitous coast, with scarcely a creek in which a vessel, even of small size, can find shelter. On the northern coast, where the Pentland Firth separates it from the Orkney islands, stand at the distance of 1 3 miles from each other the two bold headlands of Duncansby Head on the north-east and Dunnet Head on the north-west. The latter, the most northern point of Scotland, is situated in 58 40 N. lat. and 3 21 W. long., and is crowned by a lighthouse, with a fixed light, built on the rock 346 feet above the level of the sea ; while the former is marked by the white steeple of Cannisby on the west. The navigation of the Pentland Firth is attended with considerable danger, from the strength and eddies of the current. Off the island of Stroma, which is separated from the mainland by a strait three miles broad, is a small vortex called the Swalchie ; while nearer the shore are the " Merry Men of Mey," a group of breakers caused by eddies between projecting headland?. On the east coast, in addition to the harbour of Wick, erected in 1831, at a cost of above 40,000, and since improved at further expense, there is a small harbour at Sarclett and another at Staxigoe, a small pier at Clyth and another at Lybster. On the northern coast Scrabster roads in Thurso Bay afford tolerably good anchorage, while at Thurso and Sandside Bay are com modious harbours for larger vessels.
The climate of Caithness is variable, but not unhealthy; and though the winter storms fall with great severity on the unsheltered coast, yet from its proximity to a large expanse of sea the cold is not intense and snow seldom lies many days continuously. In winter and spring the northern shore is subject to frequent and disastrous gales from the N. and N.W. The waters of Forss, Thurso, and Wick, are the principal streams which traverse the county, but none of them are of any particular importance. The largest lochs are those of Watten and Cathel ; there are numerous small ones well stocked with trout.
A great change has been effected in the agricultural position of Caithness, chiefly by the late James Traill, Esq. of Hatter. The farms along the coast are still mostly in the hands of small fanners, who cultivate tbe soil only during the intervals of the fishing-season; but inland, in the more elevated districts, and along the banks of the principal streams, the land is let out into large farms, with leases long enough to encourage the holder to improve the soil and practise a rotation of crops. The average extent of land held by each occupier, in 1874, was 39 acres, much larger than the average in Sutherlandshire, which only amounted to 10 acres in the same year. In the pasturage ground, black cattle and sheep, chiefly of the Leicester and Cheviot breeds, are reared for the southern markets ; and, independently of the weekly corn-markets at Thurso and Wick, the rapidity of communication with the south is opening up a valuable market for the produce of the dairy and farmyard.
turnips ; wheat can be grown only where draining has been carried to considerable perfection. In 1874 there were only 87 acres in wheat, 1895 in barley, 70 in rye, and 27 in peas; while oats occupied 33,071 acres, turnips 14,045,
and potatoes 2190. In the same year there were 21,567