Chap. IV.

ROMAN.

203

When this machine was employed to raise water to a higher level, its diameter wasincreased to correspond with the requisite height. Round the circumference of the wheelwere attached small wooden buckets, made water-tight by properly pitching them ; themen treading the wheel turned it round, the buckets then mounted to the top full ofwater, and as they returned with their heads downwards, they discharged their contents intoa conduit prepared to receive it. Brazen buckets, each holding a gallon, were attached toa double revolving chain, and when it was required to raise the water still higher, this wasmounted on an axis, and made sufficiently long to descend to the lower level; by turning thewheel the chain was turned on the axis, and the buckets were brought to the top, wherebeing inverted, they passed their contents into conduits as before.

Water-mills were introduced at Rome , about 70 years before the Christian aera, as welearn from Strabo , lib. xii., and the first was erected on the Tiber . Antipater , who lived inthe time of Cicero, in a beautiful epigram, alludes to one of these, where he addresses themaids who were in the habit of labouring at the mill, and tells them to cease their work,and to retire to rest, to let the birds sing to the ruddy morning, for Ceres had commandedthe water-nymphs to perform their task, who, obedient to her commands, threw themselveson the wheel, forced round the axle, and by this means turned the heavy mill.

Vitruvius describes their construction as similar in principle to the tympanum; thatround their circumference were fixed floats or paddles, which, when acted upon by theforce of the stream, drove the wheel round; attached to this axis was another wheel whichhad cogs or teeth, and which turned with the water-wheel ; a large horizontal wbeel,toothed also, and corresponding with it, working on an axis, the upper head of which wasmade in the form of a dovetail, was inserted in the mill-stone. By this means the teethof the drum-wheel, which was made fast to the axis, acting on the teeth of the horizontalwheel, produced the revolution of the mill-stones; in the machine a suspended hopper sup-plied the grain by the same revolution.

Public water-mills seem to have been used in the time of Ilonorius and Arcadius, aboutthe year a. d. 398, at which time it would seem they were first established.

Mills were erected on the canals and aqueducts w'liich brought water to the city, someof which were stationed round the Mount Janiculum; we are informed that Belisarius placed upon the Tiber boats in which were contrived mills driven by the current ofthe stream ; this was done when the Gothic king Vitiges besieged Rome , and caused thesupply of water from the fourteen large aqueducts to be cut off. Procopius , lib. i. says,when the aqueducts were cut off by the enemy, the mills Tverc stopped for want ofwater; and as cattle could not be found to drive them, the Romans, closely besieged,were deprived of every kind of food, for with the utmost care they could hardly find suf-ficient for their horses. Belisarius , however, found a remedy : below the bridge whichreaches the walls of the Janiculum , he extended ropes well fastened and stretched acrossthe river from both banks ; to these he affixed two boats of equal size at the distance of2 feet from each other, where the current flowed with the greatest velocity under thearch of the bridge, and placing large mill-stones in one of the boats suspended in themiddle space a machine by which they were turned. He constructed at certain intervalson the river other machines of the like kind, which, being put in motion by the force ofthe water, drove as many mills as were necessary to grind provision for the city. Thesemills, called molina or farinaria, were generally after this time common throughoutEurope . Water-wheels put in motion by the current were very early employed to raisewater; around the paddle-wheel buckets were attached, which were carried to the topwithout the aid of treading, and discharged as we have already described.

The Water Screw , still used, is said to have been invented by Archimedes when in Egypt ,for the purpose of enabling the inhabitants to free themselves from the stagnant water leftin the ditches after the inundation of the Nile , and Vitruvius says, it was contrived on theprinciple of the screw, and raised water with considerable power, but not so high as thewheel: his instructions for its formation were as follows: — a beam, whose thickness ininches is equal to its length in feet, is made cylindrical, its two circular ends aredivided into 4 or 8 equal parts, and as many diameters drawn thereon ; these lines aredrawn in such a manner, that when the beam is laid in an horizontal position, they cor-respond with each other. The entire length of the beam is then divided into spacesequal to one-eighth part of the circumference ; thus the circular and longitudinal divisionswill be equal, and the latter intersecting lines, drawn from one end to the other, will bemarked by points. When these lines are accurately drawn, a flexible rule, made of willow,smeared over with pitch, is attached to the first point of intersection, and made to passobliquely through the remaining intersections of the longitudinal and circular divisions ;whence, progressing and winding through each point of intersection, it arrives and stops atthe same line from which it started, receding from the first to the eighth point, to which itwas first attached. Thus as it progresses through the eight points of the circumference, soit proceeds to the eighth point likewise. Fastening thus similar rules obliquely throughthe circumferential and the longitudinal intersections, they will form eight channels round