GROTTÉ D', a vast stalactite cavern in the French department of Yonne, divided into many compartments, one of which is 1200 feet long, 85 feet high, and 40 feet wide.

PATRICK D', member of the Academy of Sciences of Paris, a general officer in the French army, Chevalier of the order of St Louis, &c., was born in Ireland in 1725. His parents, in consequence of their attachment to the house of Stuart, left Ireland, and settled in France. He studied mathematics with distinguished success under Clairaut the elder, and had for his fellow-student the celebrated Clairaut the son. He obtained a commission in the French army, and in 1746 was embarked in the expedition which was intended to make a descent into Scotland. He was made prisoner, and was treated like other prisoners of war, no notice being taken of his having been born a British subject. He continued attached to the house of Stuart during the whole of his life.

In 1760 he published his Essay on Artillery. To estimate the force of the explosion of gunpowder, he employed a cannon suspended so that the arc of vibration described by it on its being fired was a measure of the force of explosion. To measure the initial velocity of a projectile, he used Robins's machine. Robins showed, that when the velocity of a projectile is great, the resistance opposed by the air is not in proportion to the square of the velocity, as is the case when the velocity is small. D'Arcy made experiments with a view of ascertaining this law, but without success. His work contains an account of experiments made by him to determine the most advantageous length of cannon. He published a paper on hydraulic machines in 1754, where he treats of the maximum of effect of water-wheels. He also published a paper concerning the duration of the impression of light on the retina. He found that the revolution of a luminous point must be rapid, so as to be performed in 1/8ths of a second at the least, in order to produce the appearance of a continued luminous circle.

D'Arcy was of a handsome figure, and passed much of his time in the gay world. A short time before his death, he married a young lady, his niece, and took the title of Count. He died in 1779.

ARDÉA, or ARDEA, a very ancient city of Latium, the capital of the Rutuli, on the river Numicus. It is now a village with 200 inhabitants, in the midst of pestilential swamps.

ARDÉBIL, or ARDÉBEHL, a town of Persia, in the province of Azarbijan, on a river which runs into the Aras or Araxes. It is situated on the southern side of the desert plain of Ardabil, which is 60 miles in length by 40 in breadth. The town contains about 500 or 600 families, and appears to have been built from some former city. It is surrounded by a ruinous wall of mud, flanked with towers in a like state of decay. It has a fort, which is a regular square, with bastions at the corners, fortified according to the European fashion. The only objects of interest are the tombs of Sheik Suffie, the ancestor of the Suffianean kings, and his descendants. It is still held in veneration as having been the residence of that prince.

ARDÈCHE, a department in the south of France, formerly Vivarais. The granitic chain of the Cevennes occupies a large part of it. The culminating point of that group is 5970 feet above the sea, and is named Mount Mezenc. Sandstone forms the lower portions of the district, over which lie beds of a coal formation, limestone, and chalk; but the continuity of these beds is disturbed by the cones of extinct volcanoes, part of the remarkable belt that passes from Pay de Dome, through Cantal and Haute Loire, towards the Rhone at Rochemare. The surface = 2081 square miles; and the population, by the census of 1851, 386,505. The department contains three arrondissements; Tournon, Largentière, and Privas. Its chief rivers are the Rhone, Loire, Cance, Doux, Erieux, and Ardèche. The mineral products are iron, antimony, coal, &c. Wine, chestnuts, and olives, are abundant, but corn is rather deficient. The mulberry is much cultivated for the rearing of silkworms.