HYDRODYNAMICS. 



409 



I 



ilistnrr der the patronage of the Ptolemies. Hippocrates, who 

 - ~."" - ' was tho first person that constructed tables of the sun's 

 motion, enabled astronomers to carry the construction 

 of Clepsydra? to a high degree of perfection ; and it was 

 probably in his time that the Anaphnrical Clepsydrae 

 were invented. Scipio Nasica, the cousin of Scipio 

 Afrk-anus, is said to have invented Clepsydrae about 

 200 years before Christ; but it is probable that he 

 :ntroduced them into Rome, for the Egyptians 

 bad used them for many purposes at a much earlier 

 period. This invention was carried to a still higher 

 degree of perfection by Ctesibius, who flourished ilu- 

 he reign of Ptolemy I'hyscus, near the begin- 

 ning of the second century before the Christian era. 

 When he was one day amusing himself in the shop of 

 her, who wai a barber in Alexandria, he observed, 

 that, during the descent of a mirror, which was coun- 

 terbalanced by a weight contained in a cylindrical 

 frame, a musical sound was emitted from the narrow 

 space between the roller and its frame. Hence he was 

 led to conceive the idea of a hydraulic organ, which 

 should operate by means of air and water. Having 

 succeeded in this attempt, he applied the same princi- 

 ples to the construction of Clepsydra, and invented the 

 ngenious machine represented in Plate CCCXIII. 

 , ami i. which is prohably the first machine to 

 which toothed wheels were applied. Fig. 5. u presents 

 -.-.tside of the machine, which consists of a cylin- 

 der standing upon a pedestal, and of two figures of 

 children, one of which allows the water to fall drop by 

 yes, while the other rises and indicates 

 ur with a wand upon the vertical line AB. The 

 cylinder AB turns round its axis once in a year, and 

 the inequality of the hours in different days is marked 

 unequal distances) of the horizontal curve lines 

 on the surface of the cylinder. In Fig. 4, whkh shews 

 the internal construction of the machine, the water rises 

 through the tube A into the figure of the infant on the 

 right hand, and is discharged from its eyes into the 

 square ranifoii M, from which it panes, by a bole 

 DMT af, into the pipe BCD. In this pipe a piece of 

 wood floats upon the surface, and by its ascent, as the 

 pipe fills, it raises the small pillar CD, on which the 

 left hand figure is made to rest, so that the wand points 

 to different hours as the float rises in the pipe. At the 

 end of 24 hours the vessel BCD i< filled, and also the 

 arm FB of the inveru.l s)phon FBK. hi.hcommu. 

 nicates with it. The *trr i- therefore drawn off by 

 the syphon, and falling in its descent into the buckets 

 of the wheel K, it puts it in motion. This wheel has 

 ix buckets, and therefore pet form* a revolution in 

 six days. Its axis carrier a pinion N of six tert '. . which 

 works into the wheel I with fiO teeth ; and th- wheel. 



n of ten teeth, drives the whet I 

 with til teeth, which, by its axis OL, turns the pillar 

 L once round in ."**>(.> days. 



nsmics was successfully cuU 



tivat- . the friend and disciple of Ctesibius. 



Beside* his treatise on mechanics, in thrre books, in 

 which he treated at length of the different mechanical 

 powers, and r- ' ,e lever, he wrote a 



work entitled fijiiri-alia or 1'n'uin/itica. which con- 

 tains in account of t' p ( n<l O f the Foun- 



tain of Compression, . 



ly called Hero'i Fountain, 



in which water was raised above its level by the elas- Hi*"". 1 ^ 

 ticity of the air, which had been condensed by the wa- '"*"*"" 

 ter. The idea of the forcing pump was probably sug- 

 gested hy the Noria, or Egyptian wheel, which con- 

 sisted of a number of earthen pots carried round upon 

 the circumference of a wheel. 



Although it has been believed, on the authority of w j*" r 

 an epigram in the Greek anthology, that water mills mMt ' 

 were invented in the reign of Augustus, yet there is 

 reason to think that they belong to a much earlier pe- 

 riod ; for Vitruvius, who flourished under Augustus, 

 and who has given a inscription of these mills, does 

 not speak of them as a recent invention. The Clepsy- 

 dra of Ctesibius indeed, which we have already descri- 

 bed, contains all the machinery of an over Jiot water mill. 

 The wheel K is put in motion by the water, which is de- 

 livered into its buckets ; and the force of the wheel is 

 employed through the intervention of wheels and pi- 

 nions, to give a rotatory motion to the vertical pillar. 



The first experiments on the motion of fluids seem Juliu* 

 to have been made by Sextus Julius Frontinus, who l-rontmu-. 

 was inspector of the public fountains at Rome under A. D. Uuu 

 the emperors \erva and Trajan. His work consist* oC 

 two short books, and is entitled, Sejrti Julii Froutini 

 i in Connlaru de .Iqneductibtit I'rliit Homer Com men - 

 tariui. It contains a full account of the different wa- 

 ters which flowed into Koine, of the nature and lurm 

 of the aqueduct* by which they were conveyed, of tin- 

 times when they were erected, of the quarters of tin- 

 city which they supplied, the number ol' public and 

 private fountains from which they were distributed, 

 and the laws which were ordained by the emperors for 

 the management ol* the public fountains. After fixing 

 the iiieaaiirn which were then used at Rome for ascer- 

 taining the quantity of water which (lowed from diffe- 

 rent adjutages, he shews, that the water which flows 

 in a given time from a given orifice does not drj 

 merely upon the magnitude or superficies of the orifice 

 itself, but also upon the height ol the fluid in the con- 

 taining vessel ; and that a pipe employed to carry off a 

 portion of the water of an aqueduct, should, according 

 to circumstances! have a position more or less oblique 

 to the direction of the current. Although Frontinus 

 was unacquainted with the true law of the velocity of 

 running waters, as depending upon the height of the 

 reservoir ; yet we may consider the foundation of the 

 science of Hydrodynamics as having been laid by his 

 experiments. As the civil engineer will naturally stu- 

 dy with a deep interest the first account which has 

 been given of one of the most important branches of 

 his profession, we would recommend, as an accompa- 

 niment to the work of Fronlinus, the three learned 

 dissertations of Raphael Fabrettus De Aquii el Aatte- 

 JucnLui retrru ROWHT, which were published in Io79, 

 and are illustrated by copious maps and engravings, t 



Although the science of Hydrodynamics is so inti- 

 mately connected with the wants and comforts of man, 

 even in a state of considerable barbarity ; yet, during 

 the dark ages, it seems to have been treated with the 

 same indifference as the more abstract sciences ; ami 

 when physics revived under the auspices of Galileo in 

 the 17th crntury, the doctrine of fluids was in the same 

 state in wti'ch it h.id been left by Julius Frontinu*. 



The attention of Galileo was in no respects particu- 



*K Hrroni. Smiriuliu tan Fred. CwuMadtai 1475, 4*. sad 1*47 cm N. AUtcti. 

 The work* of JuJhM KIOOUWM aa4 i|ilnil Fabrtttu* will bt found in Grvvii 

 j>. 130-17*\ A MW *Aui tt riMtiSHM ws paWiM bj ux Marquis Pokni iui copious BMS*. 

 VOL. xi. r*KT u. 5 



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iota. ir. 



