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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL 



[June, 



Proriietlicus. The most ancient n;ime of the river was Oceames, which 

 in the Greek pronunciation was Oceanus, afterwards called Eagle, 

 ■upon the violent eruption which covered a great part of tlie province 

 governed by Prometheus, in consequence of which he died of grief. 



What Hercules did for the low^er part of tiie Nile, Osiris did for 

 the upper part of the same river, for having come to the borders of 

 Ethiopia, he raised high banks on either side of the river, lest in the 

 time of its inundation it should overflow the cuimtry more than was 

 convenient, and make it marsh and boggy; and made floodgates to let 

 in the water by degrees as was necessary. 



Uchoreus, whom Diodorus calls the builder of Memphis, thus 

 managed the site he had chosen. The Nile flowing round the city, 

 and at the time of the inundation covering all round on the south side, 

 he cast up a mighty rampart of earth, both for a defence to the city 

 against the raging of the river, and as a bulwark against an enemy by 

 land ; on every side likewise he dug a broad and deej) trench, which 

 received the violent surges of the river, anil filled every place round 

 the rampart with water, which fortiiied the city to admiration. 



We here find Osiris, the chief god of the Egyptians, and Hercules 

 enrolled among the patrons of engineering, so that when the profession 

 is driven to a pinch for an emblem, here is the dtua ex machin/i. 

 Hercules destroying the eagle preying on the vitals of Prometlieus, 

 ■will make a pretty device either on a medal or on a service of plate 

 presented to a member of the profession. 



EMBANKMENTS OF SESOSTRIS. 



' _ Sesostris on his return from his warlike expeditions applied himself 

 like his predecessors to the adornment of his country. Among his 

 other labours are mentioned that he raised many mounds and banks of 

 earth, to which he removed all the cities that lay low and in the plain. 



CANAL OF THE RED SEA. 



The following is the account which our author gives of the famous 

 canal of the Red Sea. From Pelusiacum as far as to the Arabian 

 Gulf, and the Red Sea is a canal cut out. Necos, the son of Psameti- 

 cus, was the first who began this work, and after him Darius the Per- 

 sian cariied it on, but left it unfinished, being told by some that if he 

 cut it through the isthmus all Egypt would be drowned, for that the 

 Red Sea lay higher than Egypt. The last attempt was made by 

 Ptolemy the Second, who cut a sluice across the isthmus in a 

 more convenient jdace, which he opened, when he had a mind to sail 

 down that way, and then presently after shut up again; which contri- 

 vance proved very useful and serviceable. The river which runs 

 through this cut is called Ptolemy, after the name of its maker. 

 Where it falls into the sea, there is a city built called Arsinoe. 



_ According to Diodorus, Nile, King of Egypt, called the river after 

 his own name. For being that he cut many canals and dikes in con- 

 venient places, and used his utmost endeavour to make the river more 

 useful and serviceable, it was therefore called Nile. 



Sesostris also cut a great many deep dykes, or canals from the river, 

 all along as far from Memphis to the sea", for the ready and quick con- 

 veying of corn and other provision and merchandise, by short cuts 

 thither, for the support of trade and commerce, and maintenance of 

 peace and plenty all over the country: These canals served also as 

 defences. 



COCHLIA. 

 Our authors say that the land was watered from the canals by means 

 of a certain engine, invented by Archimedes the Syracusan, and which 

 received its name from its resemblance to a snail's shell. 



LAKE OF MERIS AND THE LABYRINTH. 



So much distrust has been thrown on the account of the Lake of 

 Meris, that we tliink it better to refer those of our readers, who are 

 desirous of obtaining information respecting it to the original, rather 

 than give it here. — The same remark we must make with regard to 

 the Labyrinth. 



WALL OF SESOSTRIS. 



Sesostris is recorded as having built a wall for the defence of the 

 east side of Egypt, against the irruptions of the Syrians and Arabians. 

 This wall is stated to have extended from Pelusium through the de- 

 serts as far as Heliopolis, and to have been fifteen hundred furlongs, 

 or about two hundred miles in length. 



PYRAMIDS. 



The Pyramids and Obelisks are works certainly belonging to engi- 

 neering, but as it is our object rather to show the bearing which 

 ancient history has upon the practice of the art in modern times, than 

 to elucidate subjects, which more properly belong to the province of 

 the antiquarian, we content ourselves with reminding our readers, that 



in the author before us they will find much information with regard to 

 these splendid works of art. 



GEOMETRY. 



Tlie priests were the instructors of youth, and the learning taught 

 by them was called sacred. In arithmetic and geometry, even in the 

 time of our author, they kept the students a long time. 



CTo be continued,) 



ON THE ACTION OF CENTRAL FORCES. 



" Happy is the man who can discover the causes of things." 



Sir — In the number for April last, there is inserted a paper on cen^ 

 tral forces, in which the writer endeavours to prove the existence of 

 "an inscrutable lavf of nature," according to which centrifugal force 

 is excited by the curvilinear motion of a heavy bodv. 



Before offering remarks on that paper, let us first inquire into the 

 distinct action of the forces that retain a heavy body in a circular 

 path. 



Taking the usual diagram, let A C D 

 be a circle of revolution, A C any very 

 small part of it, AO I) the diameter at 

 the point A, and B JI the rectangle on 

 the diagonal AC. Then AM is the 

 effect of central attraction on the body 

 at A, and AB its projectile motion. 

 The motion in A M is accelerative, 

 being originated from nothing by central 

 pressure. The motion in A B is uni- 

 form, being the result of an impetus 

 previously communicated. Now the 

 ratio of A M to A B may be diminished 

 to anv extent, by diminishing A C. For 

 AB'=AM. MD, and therefore AB : M D : : A M : AB. Now, 

 in reducing AC we reduce AB also, and the less we make AB, the 

 less is its ratio to M D or A D, and the less also is the ratio of A M to 

 AB; and this ratio may thus be diminished to any extent. Thus, 

 also, the circular motion may be considered ultimately, when A B be- 

 comes indefinitely small, to be composed of projectile motion and in- 

 cessant central pressure. Again, AC-^^AD. AM, and AB-=DM. 

 A M, therefore A C-'— A B==A M. (A D— D M) = A M-. But it appears 

 that this difference may ultimately be neglected; therefore AB^AC 

 ultimately. But AC will be the momentary projectile motion of the 

 body when arrived at C, and therefore, as the other circumstances of 

 motion are the same as at point A the new resultant and consequently, 

 also the new projectile motion ^ A C — A B. This proof holds good 

 at every other point, and therefore the motion in the circle must be 

 uniform, and equal to the original projectile motion. 



To proceed ; the writer begins with a familiar example of rotatory 

 motion in the operation of electro-magnetic attraction upon a projected 

 bar of iron. He says that its motion in the circle is uniform, because 

 the deflecting and projectile forces do not influence one another, being 

 independent of each other, and acting at right angles. Now, certainly 

 thev are independent as to origin, for the bar would adhere to the 

 magnet, though it moved not at all. But the deflecting force is de- 

 pendent in respect of ^((t/^Wi/ upon the other. We cannot certainly 

 say that the wdiole power of attraction is deflecting force, though the 

 writer says so expressly in another part of his paper, page 115. On 

 this supposition we might make the deflecting force as strong as we 

 please, other circumstances being identical ; which is absurd, and 

 would, if true, overturn entirely our mathematical demonstrations on 

 the subject, including propositions of which he himself makes use. 

 In fact, magnetic attraction may be much greater than is necessary for 

 that purpose. The deflecting force, then, strictly so called, is just so 

 much of the attractive force as is necessary for deflection, the over- 

 plus being superfluous pressure. Respecting their action at right 

 angles, I liave already shown, that the lieflecting force greatly in- 

 fluences the projectile. In fact it perpetually combines with it, and 

 produces resultants equal to one another, and to the projectile motion. 

 This is the reason of the constancy of circular motion.* 



Mystifying the origin of centrifugal force, he says that as it is equal 

 and opposite to the centripetal force, it cannot arise from the magnetic 



* He says again, the centrilugal force cannot be ihe resultant of the other 

 two forces, for it h oul.l then point within the circle This contradicts the 

 very ilcfinilion of circular motion, which is that t" 

 nor w ithout. but in the circle." 



: the resultant is neither within 



