374 



THE CIVIL ENGINEER ANU ARCHITECrS JOURNAL. 



[Deck.mbf.b, 



the vaulter, is a danperous critic for a iiudo statue; and tlie judg- 

 inent of men like these is favoural)le to hij^li art, which is thus 

 shown to he eminently fitted for the wants of a large majority of 

 the nation. An additional reason is therefore adduced for exertion 

 hy tlie artists of this country to advocate hy word and deed the 

 erection of puhlic works in sculpture of the very highest class, and 

 the selection of pictures of a like superiority for our national gal- 

 leries. 



Mr. Park then referred in very pointed terms to the practice of 

 omitting artists in the nomination of committees of taste, and the 

 selection of individuals little ((ualitied from tlieir pursuits or tastes 

 to decide in such matters. As instances of tlie doings of such com- 

 mittees, he mentioned the Nelson Monument Committee in London 

 and the Committee for the ilonument to Sir R. Peel in Manches- 

 ter. It appeared, he said, that the Manchester Committee had 

 selected a few eminent sculptors to compete, giving each fifty 

 pounds for his unsuccessful work, the successful competitor having 

 three thousand guineas placed at his disposal for the completion of 

 the work, the style of costume to he that of the present day. This 

 proceeding he characterised as at once presumptuous in the com- 

 mittee and unjust to art and artists. How dare the members of 

 that committee, he would ask, virtually pronounce that there is no 

 lurking power and talent in their own town, or in tlieir own neigh- 

 bourhood, or in the nation at large, or in the world, which an open 

 and unlimited competition on the boasted principles of their 

 vaunted political economy might have called forth, to honour and 

 advance art, to adorn their city, and to illustrate the character of 

 Sir Robert Peel. He gladly turned to tlie example of Salford, and 

 bade the men of Manchester note tlie different estimate that com- 

 mittee have of their true and just position to their constituents. 

 For the Salford Monument to Peel a competition has been an- 

 nounced also, but open to all the world, the site described, amount 

 of funds advertised, and a date for the reception of designs, leaving 

 the styles free and unfettered to the artistic skill and general 

 knowledge of the competitors. He should not be surprised that 

 Salford, fur 1500/., should get a nobler work than Manchester for 

 its .SOOO/. 



After some further remarks, the lecturer concluded by calling, 

 in eloquent terms, upon the Scottish puhlic, to show their appre- 

 ciation of the labours of the artist. He doulited not tliat it would 

 be found that the late munificence of the Legislature, and the 

 confidence of the country, would be most amply justified by the 

 foundation of a School of Art, which, like our School of Medicine, 

 would be known over the world. Much could be done by art for 

 art; but amid its noble aspirations, the Scottish public must be 

 manly and consistent in that patronage which is the aim of every 

 artist, and the only support of a national scliuol. If the glories 

 of artistic triumph are to add anotiier rose to the National Chaplet, 

 then tlie nation must be as earnest in its appreciation of the labours 

 of the artist as he will be lavish in sacrificing ease at the shrine of 

 Scottish honour, and for the glory of Scottish Art. 



MOTION OF WATER IN PIPES. 



On the. Motion of Water in Conduit Pipes; on Friction and Pres- 

 xnre in Pipe.s-; and on Jetx d'Eiiu. By M. D'Auisi isson dr \'oisins, 

 Ingenieur en chef Directeiir an Corps Royal des Mines, iSrc. &c. 

 — (Tr:mslated by T. Howard, for the Cii-il Enyincer and Arc/ii- 

 tecl's Joiiriiiil.) 



{Continued from page 165.) 



Art. III.— Op the Pressure on tub sides of Conduit Pipes. 

 Having treated of the circumstances attending the motion of 

 water in conduits, let us examine tlie effects of this motion upon 

 the pressure of the fiuid against the sides of the pipes: we shall 

 afterwards point out the most important consequences of these 

 jihcnomena. 





H3F 



Fig. 5. 



20. Let us suppose a horizontal conduit AR fitted to a reservoir 



kept constantly full. If we close the extremity B, each part of the 

 jiipe will experience a pressure measured by the height or head AC; 

 and if at some jioints H, I, K, &c., taken indiscriruinately, we 

 insert vertical tubes, the water will rise in them until the weight 

 of the columns HL, I.M, KN, be in equilibrium with the pressure 

 at these points; conseq^iently it will rise in all of them to the 

 level C I). 



Let us then open the extremity B; and suppose that the sides of 

 the pipes oppose no resistance to the motion, as in the case of a 

 \ery short tulie. and that there is no contraction at the entrance A. 

 The water « ill flow in the conduit, and will leave it, with a velocity 

 due to tlie total head A('. All the force of this head will then act 

 jiarallel to the axis of the conduit; no action perpendicular to this 

 direction will result from it, and consequently, no pressure on the 

 sides of the pipe ; as in the case of water moving in canals, where 

 there is no ]ire>sure tending to raise its surface. The fluid in the 

 tubes HL, I.M, will sink to the level of the upper part of the water 

 in the conduit. 



27. If we only partially unclose the opening B, so that the 

 orifice of discharge be less than the section of the pipe, the phe- 

 nomena will no longer remain the same. The water will be dis- 

 charged with a velocity very nearly due to AC; but the velocity 

 in the pipe will be less, following the inverse ratio of the sections. 

 Let I' be this lesser velocity, •Oljoc- will be the force or portion of 

 the head AC employed to [iroduce it: still acting on a parallel w ith 

 the axis, it will exercise no pressure ujion the sides. But the 

 remaining portion of the total force, or H — •uloJc- (by making 

 AC =: H), acting on all the particles and pervading them in every 

 direction, will press up the fluid from below at I, K, &c., and it 

 will ascend in the vertical tubes to a height equal to H — • •0155«'-'; 

 which will be limited by the horizontal KF, CE being eciual to 

 •0155)'-. Hence comes the great principle which Bernouilli has 

 established by calculation, confirmed by experiment, and which he 

 has made the basis of his Hydraulic Statistics ('Hydrodynaniica,' 

 Sectio XII.); namely: tlie pres.iiire vliick tenter running in pipes 

 exereises upon lunj (jiven point if its sides, is equal to the effeetive head 

 on that point, minus the head due to the velocity in the pipe. 



28. The resistance which the sides of the pipes oppose to the 

 motion, does not in any way weaken this principle; it only dimi- 

 nishes H, or the head which without it we should have had upon 

 the point under consideration. Let us examine this in detail. 



This lesistance is proportional to tlie length of the conduit (4); 

 that i.s, to the lengtli of the journey made by the water; thus, in 

 the same conduit it will go on progressively increasing from its 

 origin A, where it is nothing, to its extremity B where it is -00071 



Y^- (7.) So that if on BD we take FG, equal to this expression, 



as representing the resistance at B; and draw the line EG, the 

 resistances at H, I, K, &c., will be represented by the lines, ae, 



a'e\ a"e'\ &c. (since ae : u'e' : a"e" : FG : : Ee : Ee' : Eb" EF). 



Let us designate these resistances by r, r', r", R. At each 



of the points we have indicated — at I for example — the column .VII, 

 the inde.x of the pressure in a state of repose, will sink: 1st, from 

 Me (= 'OlSji''-); for in this case as in the foregoing, this portion of 

 the motive force, being directed in a line with the axis of the con- 

 duit, will cause no pressure on the sides. 2nd, from a'e' (= )•'); 

 this other part of the total force having been absorbed, and as it 

 were destroyed, by the resistance from friction between R and I, 

 could no longer have any action on this last point: the pressure 

 there will be measured simply by a'l = H — »■' — •0155«'-. In 

 general, the pressure at any given point of a horizontal conduit, 

 where ;■ represents the resistance met with from the beginning, is 

 expressed by H — /• — •0155u-. 



At the cxtreiiiity of the CDiuluit where the resistance is R, the pressure 

 Gli = H — K— 0155 !)-. If tliis extremity were quite open, we sliould have 

 ('i) R = H — "0155 »-, and consequently GB = 0; that is to say. that the 

 pressure of the extremity of ttie conduit would lie nil, and tfiat tlie columns 

 increasing the pressure at its various points will have the line £U for their 

 highest limit, 



29. Let us consider finally the case of an ordinary conduit, that 

 is, of a conduit inilined and having the extremity only partially 

 open. In a state of repose, the columns indicating the pressure 

 will be raised to the horizontal CD, the level of the fluid in the 

 reservoir, according to the Ilydrostatical law of Connnunicating 

 Tubes: they, and consequently the pressures, will he unequal; each 

 will have for measure the diflerence of level between the point 

 where it is exercised and the surface of the reservoir. When the 

 fluid is in a state of motion, these columns will undergo the same 



