giving the crew opportunity to rest from the fatigues of the voyage, and the captains to enter into new negotiations with the London merchants. Such is the animated spectacle presented by the Thames below London bridge. It was impossible to construct new bridges without materially interfering with commerce. Again, the inhabitants of the docks, an eminently commercial and populous quarter, and the resort of vessels from every part of the known world, were unable to reach the opposite side of the river, except by crossing it in boats, or going a distance of two miles and a half to reach London bridge."

Various fruitless attempts were made at different times to open a passage under the Thames, but the masses of stone encountered, and the falling in of the earth, caused them all to be abandoned.

In 1824, the execution of this subterranean passage was intrusted to Brunel. This tunnel consists of a double and capacious archway. The shaft at this place is one hundred and fifty feet from the river. It was formed by building a cylinder of brick-work, fifty feet in diameter, forty-two in height, and three in thickness, on the top of which a steam engine was erected for raising the water and earth. The cylinder was let down bodily into the ground, forcing its way through a bed of gravel and sand, twenty-six feet deep, and full of land water. The shaft was sunk to the depth of sixty-five feet, and from this level, another smaller shaft, twenty-five feet in diameter, was sunk, destined to be a well or reservoir for the drainage of water. The excavation for the body of the tunnel was commenced at a depth of sixty-three feet, and was carried on at a declivity of two feet and three inches per one hundred feet, in order to have sufficient thickness of ground to pass safely under the river. The excavation is thirty-eight feet in breadth, and twenty-two and a half feet in height, presenting a sectional area of eight hundred and fifty feet, and the base, at the deepest part of the river, is seventy-six feet below high-water mark. The body of the tunnel, and in fact every part, is of brick-work. The ex

pense is estimated at twelve hundred pounds sterling per yard, and the entire length is thirteen hundred feet.

One side is appropriated to carriages passing in one direction, and the other to those passing in the contrary, with paths for foot-passengers by the sides of the carriage-road. The middle. wall, between the two archways, was first built solid for greater strength, but openings were afterwards cut at short distances, so that each has a ready communication with the other. The two shafts at the extremities will contain easy flights of steps for foot-passengers.

The means by which M. Brunel effected this perilous excavation, consisted of a powerful apparatus of iron, which protected the labourers from danger of accidents, and received the characteristic name of shield. It was formed of twelve great frames lying close to each other, and severally provided with the mechanism necessary to move them forward, and to secure them when stationary, against the brick-work. The frames were twenty-two feet in height, and about three feet in breadth, and each divided into three stages or stories; the whole thus presenting thirty-six compartments, each capable of holding a workman, who operated upon the surface opposite to him; and when from three to six inches were thus removed over the whole surface of the shield, the frame was moved forward, and the work secured by immediately adding so much more of the brickwork to the body of the tunnel.

Besides his labours in this branch of art, this illustrious French engineer has rendered eminent services to many mechanical arts. The most remarkable mechanical sawing-machines, are those established by him in the Woolwich and Chatham arsenals in England. A few years ago, M. Brunel invented. some circular saws of large size, which are very convenient for cutting thin layers of wood for veneering. These saws are about six metres in diameter; they reduce the wood to two millimetres in thickness, with such precision that it afterwards requires no polishing.

CHAPTER LXIV.

GYMNASTICS.

HE ancients, our superiors in almost all things, considered gymnastic exercises as an important branch in the physical training of youth. These exercises, in fact, give the limbs qualities which they have not received from nature, whilst they develope those faculties already possessed. In modern times, especially since the invention of gunpowder, gymnastics have been neglected and almost forgotten.

Pestalozzi endeavoured, in the last century, to bring them again into use; he demonstrated their utility and importance, and from that time many others, men of science and information, betrayed an interest in this part of education.

Colonel Amoros, a Spanish refugee, was the principal, the most active, and the most intelligent promoter of gymnastics as connected with the physical education of children. He founded a fine establishment in Paris (1819), known by the name of the Amoros Gymnasium, in which he endeavoured to develope the physical strength and agility of children. His efforts were rewarded by a most astonishing success, and the government, convinced of its efficacy by the results, contributed to the support of so valuable an institution. Similar establishments were rapidly founded in all parts of the civilized world. Gymnastic exercises were introduced into many schools, and especial institutions formed where young soldiers benefit by the various exercises.

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CHAPTER LXV.

ARTESIAN WELLS.

HE gushing fountains called Artesian wells, were known in very early ages, and are still found in the deserts of Asia, in India, in China, &c. For the last century they have existed in Lower Austria, and in Modena and Bologna, as well as in the forest of Urbain, where Cassini

bored. The most ancient Artesian well known in France is that of Lilliers, in Artois, which was bored, it is said, in 1126. In 1780, Louis XVI. caused one to be bored under his direction at Rambouillet.

It is supposed that the name of Artesian proceeds from the fact that the first wells of the kind known in France, were in the province of Artois.

They are bored for with a miner's plummet, and by the intervention of divers instruments, we are able to perforate strata of great thickness. The water rises to the surface with violence, and in some situations of so pure a nature that no other is used for domestic purposes.

The Artesian wells have lately been successfully sought for in all parts of France, and in the southern part of England. We look for these wells only in the neighbourhood of mountains; where the soil is not granitic or schistic, or consisting of permeable strata of sand, of pebbles existing under strata of clay, chalk, or beds of stone without crevices or fissures. The attempt to produce one in the Grenelle slaughter-house shows that boring for them is sometimes no easy task; for seven years, the mechanician Mulot has been occupied in boring under the direction of M. Arago, and although the ground has been penetrated to a great distance, no water has been found.

CHAPTER LXVI.

AGRICULTURAL INSTRUMENTS.

URING the long years of peace which have occurred since the downfall of the empire, the fabrication of agricultural machines and instru

ments has become of great importance. "Not only," says M. Charles Dupin, "have the workshops of this kind increased in number, but the articles themselves have improved materially. A knowledge of geometry has done much towards assisting this branch of art. Works upon the application of this science to the arts have been published, tending to propagate the theoretical knowledge indispensable to practice. These lights have been communicated to the workmen of every rank, down to the commonest and humblest. Many of these workmen, assisted by their new scientific attainments, have made rapid advances in their career."

Among these the most remarkable is the farmer's boy, Grangé, who has invented a plough upon a simple but excellent idea, having the twofold advantage of requiring but a small motive. force, and of being easily guided by the least experienced labourer. Baron Dupin speaks as follows of M. Grangé's invention :

"A farmer's boy in the department Des Voges, called Grangé, proposed a plan for the improvement of the plough in common use, that which has a beam. Being himself a field-labourer, he was well acquainted with the fatigues and inconveniences inseparable from that instrument. By dint of study and experiments, he succeeded in discovering a simple method of overcoming the great difficulties incurred in ploughing a stony and un