6:^ 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[February, 



sum of the two motions is greater tlian tliat which a body would 

 aocjiiire by its simple descent. \V'lierefore, since the aforesaid 

 force liy ]iressinfjf, generates veh)city and motion distiiu't from tliat 

 whicli a body, in descending, generates ; in like manner it is ap- 

 plicalde to water pressing on the lower films, and by jiressing, com- 

 nmnicating additional force to them. Besides, there are other 

 reasons corroborative of this truth, among whidi is the fact, that 

 it is necessary to spread the accelerated velocity <if water passing 

 from a larger to a narrower section over a mean of pressure. 



Galileo says, " I have been carefully considering and going 

 through various problems to investigate the acceleration of water 

 having to pass through a narrower channel, also whether it has the 

 same declivity in both." The greater nund>er of authors sidve the 

 lioint by increasing the height of the water, and lience the pres- 

 sure, thus generating a greater velocity. Eustace Manfredi thus 

 expresses himself :^ — " The same water passes through a lesser as 

 through a greater section, wherefore it is forced to pass with a 

 greater \elocity, precisely as will be the case in a vase in which 

 the surface of the water maybe at a certain height above the sum- 

 mit of the aperture." Guglielmini, to the same effect : — " The 

 Tipper parts press the lower, and oblige them to receive a force, 

 wliich being compelled to act, produces the same degree of velocity 

 which the descent winild have given them." VVe might quote 

 other authors, who account for the increased velocity in narrower 

 sections by having recourse to the pressure generated by the height 

 of the upper parts, only they are in doubt on this subject, whether 

 to attain so great a velocity it be necessary that the upper w ater 

 should increase in height till it becomes stationary; not being able 

 to believe that the upper water which is in the act of running is 

 capable of producing a new increment of velocity in the lower. 

 But experience teaches us that if the breadth of a section be 

 diminished one-half, the water will not rise that half, as would 

 appear necessary ; if the velocity does not increase, it increases 

 at least very little, either in section or at the base, where the re- 

 duced sections are of the same breadth, since the water retained 

 by the narrowing of the piers of a bridge is but slightly raised. 

 Wherefore it is necessary that the velocity increase without having 

 regard to any new inclination, which is always the samc\ but only 

 by an increase of height, which causes a pressure on the lower 

 water which is in the act of running ; wh^ice I deduce the argu- 

 ment to strengthen my opinion in the ease in which the velocity, 

 arising from the inclination, is equal or greater tlian that which 

 might have been generated by the pressure. Let us take two cases, 

 one which allows the same measure of water to pass through mie 

 section twice as little as the first, preserving the same inclination, 

 the other in which the \ elocity increases till it becomes twice as 

 much. 



But whence comes such an increase of velocity .'' what is the 

 principle, what the nature of it ? To say with Gennete, that twice 

 the quantity of water doubles the velocity, is not to adduce a proof 

 but to advance a mere assertion, which either supposes or requires 

 it. I do not think that a true philosopher w ill jiereeive in the in- 

 crement of so nmcli water the principle of so great an acceleration. 

 It behoves us to examine the genesis of such a plienomeuon, and 

 to observe the mechanism wliich nature ado]its therein. And, 

 firstly, two epochs of time are to be distinguished, one the first 

 perceptible moment in which the section is reduced to half. Now, 

 at this first instant, the water must swell and rise much above its 

 first leveL, in which rise it generates a proportional velocity. But 

 in the very act in which such a velocity is generated, the water 

 begins to fall, wlierefore the present case holds good, that the sec- 

 tions are in reciprocal projiortion with the velocity. The water 

 does not fall in this manner, wherefore it returns to its first level, 

 or a little higher, there being a cimstant princijile which compen- 

 sates for a portion of the ^•elocity destroyed by successive obsta- 

 cles. AVater in its course meets w ith continual resistance which 

 diminishes its force, wherefore there remains in the water a con- 

 stant jiriiiciple whicli supjilies and renews any decrement of velo- 

 city wiiicli tlie resistance may produce. Now this principle is, that 

 whatever small increase of height above the (o-igiual level causes 

 pressure causes also velocity. Arrived at which point the water 

 m/iintains the same height, which I have elsewhere designated 

 equilibrium and constant state. Observers have not paid attention 

 to the first epoch in which the water swells, is agitated, balances 

 itself, but only have considered the other in which it acijuires equi- 

 librium, state, law. All this takes place so quickly tliat the swell- 

 ing, sinking, and equilibrating hardly are evident to our percep- 

 tions. U\ as 1 believe, tlie experiments of (iennete were true, 

 according to which a river doubles or triples its water without 

 raising its level, then it would be correct to say that it was free 

 from any sensible resistance. This might be the case in an artifi- 



cial river of short length, over a level bottom witli smooth sides, 

 and furnished with clear water. But in a natural and turbid 

 stream, ivhere the resistance, and that considerable, will never be 

 wanting, it is not likely that when reduced to half its original 

 section, it preserves its former level. This being determined, to 

 come to the ipiestion above jiroposed, I residve it thus : — Either 

 the velocity begins to increase by the water lieginning to swell, or 

 the whole mass increases. If the first takes place, then the height 

 being small, and hence the pressure being likewise small, the velo- 

 city generated will be also small. It is not that so small a velocity 

 is added to so great, which it derives from an inclination, contrary 

 to the sentiment of S'Gravesand. If the second takes phu-e, it 

 being then the velocity which increases, is eipial to, or is less than 

 that which results from an inclination, and not having any other 

 generating principle than the pressure, it is clear that it acts when 

 the velocity which generates itself is less or equal to that which 

 was before generated by the inclined plane. Now I repeat, there- 

 fore, that the water as it strikes the bottom presses the lower films 

 which run, sjiread out upon it, by which the pressure is communi- 

 cated from abo\'e downwards. I agree with what Manfredi says, 

 that " all the low er strata of water may be regarded as so many 

 bottoms, or actual planes, with regard to the upper planes which 

 run upon them. Hence these fluid planes are sensible of the same 

 pressure of running water which they would sustain if it were sta- 

 tionary at an eipial height." To me it appears an incontestable 

 truth that water which presses the bottom should press all that 

 portion by w Inch the pressure is communicated, otherwise if it does 

 not press all that which forms the middle, it will never arrive at 

 the bottom of it, which is contrary to all experience. If this bot- 

 tom be of a cur\ ed form, concave towards the water, the pressure 

 will have the action of a centrifugal force, the « Inch conspiring 

 with the former, will increase the momentum, and thereby its 

 energy and velocity. 



FROCBEDINGS OF SCIENTIFIC SOCIETIES. 



ROYAL INSTITUTE OF BRITISH ARCHITECTS. 



Jan. 10. — Charles Fowler, Esq., V.P., in the Chair. 



Many presents were announced. Among them were drawings from .\Ir. 

 B. Peny, of tlie Town Hall uf Mor()etli, supposed to be by Vanbiugli, and 

 a work on church building by M. tie Lassaulx of Coblentz. 



Mr. Layard, the explorer of Isiiieveh, was then introduced by Mr. Tite, 

 and at the request of the Institute, made son.e remarks on the ruins of that 

 city. Of the external architecture, or of the date of the ruins, he could 

 ssy little, as hardly a fragment remained to guide the judgment, though no 

 doulit of their great antiquity could be entertained. One proof he could 

 give was, that though the earliest ruins were buried in the soil, graves had 

 been dug in these by a people who lived 700 years before the coninion erii. 

 He was inclined to believe that some of these buildings might be three thou- 

 sand years old. The rooms were covered with marble sl.ilis, sculptured in 

 low relief, like those in the British Museum, and they were joined together 

 hy double dovetails of iron, and the doorways were flanked by tall winged 

 fiuures, higher tlian the side slabs. Ihe figures were all marked with blood, 

 as if it had been thrown against them, and left to trickle. The walls whicli 

 back the slabs are of sun-dried biieks, and, where they show above the 

 slabs, are plastered over and painted. Such beams as remain are found t(» 

 be of niulheiry. How the slabs have been preserved is a matter of mysleiy, 

 but is perhaps to be exjilained by their lying under the crumbled remains of 

 the bricks, which have returned to earth. Mr. Layard noticed ihat the 

 buildings were pro\ided with a system of sewage, a drain running from each 

 room to a main sewer. In a small cliamber which he bad discovered anieng 

 Ihe ruins, he hail seen vaulting of bricks regularly arched. The date of the 

 destruction of Nineveh wiis 700 years B.C., while the bas-reliefs belong to 

 earlier dates. In many cases the slabs have been used before ; one slab was 

 found wilh the sculptured face turned to the wall, and the back re-worked. 



Mr. BoNOMi observed that in Egypt the cramps were of wood, and he 

 thought it exlraordinary that at Nineveh tliey should be of iron. 



Mr. Donaldson remarked that those ol the l^aitbenon were of iron, and 

 oroceeded to otter his tribute of tlianks to Mr. Layard for his communica- 

 tions. He thought that gentleman the nioie deserving of praise, as so mm h 

 of what lie bad dune was by his own labour and expense, and yet he had 

 successfuUv comjieted with the explorers sent out by the French govern- 

 ment. Mr. Donaldson wished to inquire whether the external face ot the 

 sun dried bricks were covered with plaster to keep out the wet. 



Mr. LaVaRD hail not observed this. The internal face was partly coloured 

 and enamelled, and decorated with human figures and other ornaments. As 

 to the vaulted chamber of which he had spoken, it was covered with an 

 arch of 12 or 14 feel diameter, very nearly a semi-arch. As to the sewers, 

 ihev were not arched. 



