Discussion. The Royal Border Bridge Over the River Tweed, on the York, Newcastle and Berwick Railway.

Abstract

J E f i = 51 v9 X 4 = 46.7 inches, mean velocity.The following Table shows at a glance, the results arrived at by both methods, and also by the experiment. I I Velocity in inches per second. IExperiment.-- 51.00 46-70Here it will be seen, that though Du Buat and Eytelwein both give results higher than the experiments seem to warrant, yet Du Buat is nearer of the two.Mr. HAWKSHAW thought, that although the Paper entered minutely into the method of making the foundations, and of framing the centres and timber-work generally, it did not sufficiently describe the mode of putting the masonry together.As far as he could understand it, the piers appeared to consist of a facing of ashlar, with a hearting of rubble, very few through-courses being used to connect the faces of ashlar. This mode of construction he considered to be bad in principle, and that it W" safer, where large stones were used, to leave out the hearting altogether, or else to build the pier entirely of rubble. H e had adopted both methods; he had, on the one hand, used large stones tied across in several places, so as to leave voids; and he had built a viaduct 130 feet high, entirely of rubble. There was more risk, when very large stone was used for the outside work, and small stone for the inside work, and some failures had been due to this cause, as an unequal settlement was almost sure to et~suc. large viaduct a t Barentin, which was built in the mixed mode stated to be so objectionable. T h e piers of that viaduct were built of ordinary mortar, the arches being afterwards set in cement, and when the failure occurred, the arches gave way in large masses, but the bricks of the piers were all separated, and so perfectly free from mortar, as not to require cleaning, previous to being used again. I t was most important in making mortar, that every particle of sand should be coated, as it were, with the hydrated lime, so that every interstice between the grains might be filled up: its quality also depended upon the proper selection of materials, as well as on their perfect manipulation.Captain W. S. M O O R S O M thought, that the great difficulty of making good mortar, arose from the circumstance, that the lime and sand were obtained from so many different localities, and that each locality required a different mixture, which could only be properly determined by repeated trials; it would, therefore, be frequently found, that an adventitious mixture was the best. He could not understand why the span of the arches should have been fixed at 61 feet 6 inches. Time had probably been an element in considering the span to be given to the land arches, but in the river arches where so much difficulty had been experienced in getting in the foundationsi he thought it would have been preferable to have constructed the arches of a larger span, thus diminishing the number of foundations required. This plan would also have had the advantage of causing less disturbance to the course of the river.Mr. W. RADFORD thought, that mechanical agitation was most important w...