Fig. 24.
“It is the part of a channel sluice or a sewer on which the water flows; it is the bottom, which ought to be formed so solidly that the force of the current cannot disturb it. The beds of sewers, therefore, should be made of good flat stones, or, which is still better, of hydraulic cement, when it can be procured, because the water finds its way between the joints of the stones; while, if the cement is properly used, it forms along the whole channel one homogeneous mass perfectly water-tight. Besides we take care to give to the bed of a drain a section slightly concave, joining its walls without angles; for water takes advantage of angles to effect its work of destruction. Angles, moreover, are not easily cleared out when subterranean channels have to be cleansed. The best form to give to a sewer is the one given here in section (Fig. [24]).
CHAPTER X.
PAUL BEGINS TO UNDERSTAND.
In spite of the news of the war, which was daily assuming a more threatening character, M. de Gandelau insisted on the works not being interrupted; and the inhabitants of the château found in the execution of the plans prepared by Eugène and Paul a beneficial distraction from the sad forebodings which oppressed them.
In the evening, after reading the paper, which recorded, alas! only a succession of disasters, everyone remained silent, with eyes fixed on the hearth; but soon, with a determined effort, M. de Gandelau started the inquiry how the house was getting on. It was for Paul, as Clerk of the Works, to give an account of the operations of the day, and he began to perform his task with a fair amount of exactness and clearness. He showed his memorandum books, which, thanks to Eugène’s corrections, were not very badly drawn up, and which, by the help of a daily summary of accounts, indicated the expenses that had been incurred.
Fig. 25.
The excavations had hitherto furnished enough materials to obviate the necessity of sending for any from the neighbouring quarries. About the 15th of September the cellar walls were already beginning to make their plan visible, and it was time to think of the exterior plinths in elevation, and of the cellar vaultings, for whose construction wooden centres were required. The carpenter was therefore commissioned to send for timber-sawyers, to convert some trunks of poplars, which having been cut some time before, were put by for the purpose. The best part of the wood was sawn into thin boards for battens, to be employed when required; and the slabs—that is, the part near the bark—were cut up for centring for the cellars. As the plans gave only two barrel-vaults whose arches were different, the curves were soon struck out, and the carpenter prepared the centres, which were fixed up as soon as the cellar walls reached the level of the spring of the vaults These centres were formed in the manner shown in Fig. 25—that is, consisted each of a tie-piece, A, a king-post, B, two blades, C, and clips, D, which held fast the curves formed of slabs of poplar nailed together, as shown at E, and fixed at G and H on to the king-post by means of a notch, F, and to the tie-piece by an iron staple. On these centres, supported by props K, and set five feet apart, they laid a covering composed of planks, L, 3 inches thick, to receive the vaults, which were made of blocks of tufa extracted from the banks of the rivulet, 8 inches in thickness, with a good layer of mortar over all. The openings for the air-holes had to be contrived in the haunches of the vault, a piece of work which gave Paul considerable trouble—or rather, he had some difficulty in understanding it and sketching it in his note-book; for, as to Branchu, he did not seem to find any particular difficulty in it.
Eugène had given the sketch for the air-holes at the same time as the section of the plinth, 5 feet in height above the ground level.