204

HISTORY OT ENGINEERING.

Book I.

the shaft, in the form of a screw. To these rules of willow others are attached, also smearedwith liquid pitch, and to these others, until the thickness of the whole be equal to one-eighth part of the length. The slips or rules fastened all round are saturated with pitch,and bound with iron hoops, in such a manner that the water will not injure them. Theends of the shaft or axle, also strengthened with iron hoops, have iron pivots inserted intothem.

On the right and left of the screw are beams, with a cross-piece both at top and bottom,into which is inserted a gudgeon of iron, in which the pivots turn. Men are employed totread it in the usual way, and by this means the screw is made to revolve The inclinationat which the screw is worked is at an angle of forty-five degrees ; for if the length isdivided into five parts, three of these will give the height that the head is to be raised; thusfour parts will be the perpendicular to the lower mouth. Although the above is thedescription left us of this instrument or machine, as it was in use by the Romans, in allprobability they found out at an after period, that it was not essential to preserve the in-clination to one angle, but that it might be either more or less than that of forty-fivedegrees, for the nearer we approach to a right angle with the cylinder, the more thehead of the cylinder may be elevated, and the higher the water will be raised. It is, how-ever, necessary that in inclining it, the channels should decline somewhat from the plane ofthe horizon, that the water may, as the screw turns, continually descend in its course.When many channels are used, they must of course be made narrower than where there arefew, in order to preserve the same inclination, so that less water will be raised by each re-volution of the machine.

IIow the tread-wheel was attached to the cochlea or screw wc are not informed, the menemployed must have been able to preserve tlieir upright position, and probably an additionalwheel was provided for the purpose.

Machine of Ctesibiu s for raising water to a considerable height. About 150 years beforeChrist, the mechanical arts had made considerable progress in the school at Alexandria, andmany of the principles left by Archimedes were studied more fully, and brought into prac-tice ; at this time the common pump seems to have been partially, if not thoroughly,known ; and its principles must have been understood before the more complete forcing-pump, which was the invention of Ctesibius . Vitruvius has left us a description of thismachine as used in his day. It was made of brass ; at the bottom were two buckets, neareach other, with pipes annexed in the shape of a fork, united to a basin in the middle. Inthis basin were valves, neatly fitted to the apertures of the pipes, which, closing- the holes,prevented the water, which had been forced into the basin by the pressure of the air, fromreturning. Above the basin was a cover like an inverted funnel, riveted so securely onit, that the water could not, under any pressure, force it oft'. On this was fixed an uprightpipe, called a trumpet.

Below the lower orifices of the pipes the buckets were furnished with valves, over theopenings below.

Pistons made round and smooth, and well oiled, were fastened to the buckets, andworked from above with bars and levers, which, by their repeated alternate action, pressedair into the pipes, and the water being prevented from returning, by the closing of thevalves, was forced into the basin through the mouths of the pipes, whence the force of theair, which pressed it against the cover, drove it upwards through the pipe ; by this meanswater on a lower level might be thrown into a reservoir for the supply of fountains.

Ctesibius , the greatest mechanic of antiquity after Archimedes , invented a clepsydra, orwater-clock, an air-gun, and some others which, as Vitruvius observes, prove that liquidsin a state of pressure from the air produce a variety of effects, and for their descriptionrefers to the writings of that philosopher, which were extant in his time.

This pump was in all probability the very same in its application of force to the modernfire-engine.

Hydraulic Organs _These were blown by the action of water, and it has been doubted

whether they were not played by the fingers by means of keys; the description given usof such an organ by Athcnaeus is that it was invented in the time of Ptolemy Euergctes byCtesibius , and that the idea was first given by Plato , who invented a clepsydra or water-dial,which played upon pipes the hours of the night at a time when they could not he seen bythe index : the descriptions left us by Vitruvius are not sufficiently clear to enable us tocomprehend its construction ; that by Claudian indicates that it resembled a modern organ,blown by water instead of bellows.

Saw Mills for cutting Slabs of Marble were invented, as Pliny tells us, in Caria , to cut themarble employed to encrust the palace of Mausolus , king of Halicarnassus , as early asyears before Christ. The sand which Pliny says was employed for this purpose was thecutting power, and not the saw, which was used for merely passing down the sand, andrubbing it against the marble; the coarser the sand employed, the longer the time neces-sary to polish the marble, and Cornelius Nepos tells us that Mamurra, who was born atFormia , and employed to superintend the labours of the masons, smiths, and carpenters,