HYDBAULIC-EAM OE WATBR-HAMMEE. 85 



fact that in addition to the weight of the pipe aud water, and before this conld be raised, 

 it was necessary for the ram to exert such additional force as would tear asunder the leaden 

 joints at C and D and loosen all the others. AVhat this additional exertion may be equi- 

 valent to, I am not in a position to state, without some experiments on the longitudinal 

 adhesion of pipes thus leaded and staved in a way to prevent leakage under a 466-feet 

 head of water ; biit it must be assumed at more than the 200-lbs. pressure per square inch, 

 exerted by the water, through the gasket, on the leaden band enveloping the spigot end 

 of the pipe. This, at live-feet aA'^erage girth and half-inch thickness, under the aforesaid 

 pressure, is equal to 6,000 lbs., and as there are ten joints between A and 0, B and D (those 

 between C and D not having started), it would appear that an additional strain of some 

 60,000 lbs. must have been exerted in order thus to dislocate the conduit simultaneously 

 at the several joints just mentioned. But this pressure of 200 lbs. to the inch must, of 

 course, have been exceeded, since leaden joints do not give under it, and no doubt more 

 than twice that pressure must have been exerted, to say nothing of the force required to 

 thrust the pipe at C, as already stated, through the three-inch deal-lining of the box and 

 some six inches into the space beyond. 



This accident teaches three important lessons : — first, the necessity of having double 

 or treble gearing to all such gates, as pipes under great heads of water are supplied with, 

 that it may be impossible for them to shut at a speed beyond a given velocity ; secondly 

 the possible and probable efl'ects of a water-ram or hammer on unloaded or unconfined pipes ; 

 and lastly, the necessity, where it is unloaded or not buried in the earth, of securing the 

 conduit both vertically and laterally to the bed on which it rests, in order to prevent the 

 recurrence of an accident which, in some cases or localities, or under certain circumstances, 

 might prove highly disastrous. I have often stood with my men in this tube at, or very 

 near to, the point C, where there is an air A^alve, and had such an accident occurred there 

 then, we must, in a second, have been caught and crushed to atoms between the conduit 

 and the tube. 



The damage has been repaired by merely thrusting back the pipe at C and D into 

 position, by re-running these two joints and re-staving all the others ; for, strange as it may 

 seem, not a single break or flaw or the slightest crack, occl^rred at any point in any of the 

 pipes which together make up the length of 140 feet. This pipe will, when the other is 

 laid side by side with it, as intended in the new iron tubular bridge, be tied to it by iron 

 straps, and both will be fastened down to the iron floor-beams of the bridge. 



It may also be interesting to engineers to know that, some years ago, the whole super- 

 structure of this bridge was thrust bodily aside some three feet at the centre, owing to the 

 pressure of ice piled up against it, the pipe, of course, moving with the bridge and partak- 

 ing of the same lateral displacement. This lateral motion did not start any of the joints, 

 beyond a mere oozing of the water from some of them, the plastic nature of the lead sub- 

 mitting to this displacement, without any other effect on the passage of the water through 

 the pipe. The bridge was again thrust back into its normal position and vertical plane, 

 by the simultaneous use of a number of jack-screws applied to the lower side of the bridge 

 superstructure, — these screws abutting and acting against as many struts of stout timbers, 

 the lower ends of which rested on the stony bed of the river. This displacement of some 

 three feet in seventy (half the span), or about five per cent., without materially loosening 

 the joints, indicates the possibility of doing at least as much in any case, where it might 



