Chap. IV.

ROMAN.

205

attached to the army of Osar in Gaul, was the first Roman who covered the walls of hishouse with slabs of marble.

Measuring Distances when Travelling , Vitruvius says, was discovered by the ancients,and found useful in his time ; his account exhibits the manner in which such mechanismwas employed at sea and on land. When adapted to a chariot or travelling carriage, thewheels were made of such a diameter, that every revolution would advance the carriage12.^ feet, thus 400 revolutions passed over 5000 feet, or a Roman mile; the diameter ofthe wheels was therefore nearly 4 feet. A drum wheel was securely fixed to the innerside of the nave of the wheel, which had one small tooth projecting beyond the face of itscircumference ; and on the body of the chariot was a small box with a drum wheel,placed so as to revolve perpendicularly, and fastened to an axle. This latter wheel wasequally divided, on its edge, into 400 parts or teeth, which corresponded with the teeth ofthe lower drum wheel; besides this, the upper drum wheel had on its side one tooth pro-jecting out before the others. Above, in a third enclosure, was another horizontal wheel,similarly toothed, and which corresponded with that tooth which was fixed to the side of thesecond wheel. In the third wheel, just described, were as many holes as arc equal to thenumber of miles in an ordinary day’s journey. In all the holes were placed small balls, andin the box or lining was made a hole, having a channel, through which each ball might fallinto the box of the chariot, and the brazen vessel placed in it: as the wheel turned round,it acted on the first drum wheel, the tooth of which, in every revolution, striking the toothof the upper wheel, caused it to move on, so that when the lower wheel had revolved 400times, the upper wheel had revolved but once, and its tooth, on the side, would have actedon only one tooth of the horizontal wheel; 400 revolutions of the lower wheel caused theupper wheel to turn but once, and thus showed that 5000 feet, or 1000 paces, had beenperformed. By the dropping the balls, and the noise they made, it was known whenthey had performed a mile, and at the end of every day’s journey, the number of balls col-lected in the bottom showed the number of miles passed over.

In navigation, nearly the same means were used; but an axis passed across the vessel,projecting over each side; to this were attached wheels four feet in diameter, withpaddles dipping into the water. That part of the axis within the vessel had a wheel witha single tooth standing out beyond its face, at which place a box was fixed with a wheelinside it having 400 teeth, equal and corresponding to the tooth of the first wheel, fixed onthe axis. On the side of this also, projecting from its face, was another tooth. Above, ina box, was enclosed another horizontal wheel, also toothed, to correspond to the toothfastened to the side of the vertical wheel, and which in every revolution, working in theteeth of the horizontal wheel, and striking one each time, caused it to turn round. In thishorizontal wheel were holes, wherein the round balls were placed, and in the box of thewheel was a hole with a channel in it, through which the ball descending fell into thebrazen vase, and made it sound. A vessel impelled either by' oars or by the wind gavemotion to the paddle wheels, which, driving back the water forced against them, turnedthe axle round, and the drum wheel followed, whose teeth in every revolution acted on thetooth of the second wheel, and produced moderate revolutions. "When the wheels werecarried round by the paddles 400 times, the horizontal wheel had made one revolution, bythe striking of that tooth on the side of the vertical wheel, and thus in the turning causedby the horizontal wheel, every time it brought a ball to the hole it fell through the channel.By sound and number were found the number of miles the ship had passed.

In the early Italian editions of Vitruvius , particularly that by Caesar Cesarinus, wood-cuts exhibit these paddle-wheels attached to the sides of the vessels.

Hydraulic architecture is greatly indebted to the Italian engineers, who have beensuccessively employed in draining the marshes of Italy , confining the rivers to their naturalbounds, and the ocean to its limits ; before the seventeenth century there were scarcely anyprinciples laid down to direct the civil engineer, and Europe could hardly boast of anyeminent man in that profession. Rome had left marks enough of her greatness: as faras construction went, or the handling of materials, there could be no want of models toguide the labours of the artificers ; in building, enough was to be found to imitate, bothin the science and the art. But hydraulic architecture had been neglected; the rivers,in consequence, were left to pursue their natural course, their beds became elevated,and their openings to the sea silted up : all the ancient harbours were for the most partdestroyed or unfit for the reception of vessels of larger burthen, which commerce had intro-duced.

Lombardy , the richest district in all Italy , and with a soil more fertile than any other inEurope , is watered by the Po, which receives its supply from both the Alps and Apennines ,and has its course for upwards of a hundred leagues through Sardinica, Pavia, Placentia,Cremona, Mantua, and Ferrara to the Adriatic Sea ; its importance is so great, that it isnavigable to Turin .

The snows which cover the mountains that bound Lombardy during the summer afford