328 PLANS OF RESIDENCES 



and six feet will be a sufficient clear width inside. For an alley 

 fifteen feet wide, the arch should be eighteen feet long. The steps 

 down to it, and their flanking walls, would make a length of ten to 

 fifteen feet more on each side — depending on the manner of the 

 descent, and the nature of the superincumbent improvements — and 

 likely in any case to make the entire excavation upwards of forty 

 feet in length, including the slopes for the steps. The side-walls 

 throughout should be double or hollow walls ; the inner one of 

 brick, nicely pointed, the outer one of stone, and both made water- 

 tight with water-lime cement. The arch over the tunnel proper 

 should be made with great care to render it perfectly water-tight 

 also ; and if the entire filling above the arch, and on the outside of 

 the side-walls, is made with good gravel, broken stone, or coarse 

 sand, so as to let all surface water soak down directly to the drain 

 below the floor of the tunnel, there will be little liability to excessive 

 dampness or dripping water in the tunnel. The arch for the main 

 tunnel on this plan is to have the springing points five feet from 

 the floor, and to be that segment of a circle which will make the 

 centre seven feet high. For stairs, broad solid stone steps are of 

 course the best in the long run, but some expense for such work 

 may be saved by having the slope down to the tunnel floored with 

 a smooth water-lime cement, and a flight of plank steps put in, 

 supported at the ends only, and high enough above the sloping^ 

 cement floor to allow the latter to be readily brushed and kept 

 clean under the plank steps. These, having the air circulating- 

 freely all around them, will not be liable to quick decay. 



In the plan under consideration, the walk leading directly from 

 the rear arcade of the double-house to the grape-house is to de- 

 scend gradually for about twenty feet, so that at the front line of the 

 latter it will be two feet below the general surface, and a step on 

 the same line will drop eight inches more to a stone landing, from 

 which four steps up on each side lead to the two sides of the grape- 

 house, and ten steps down, to the floor of the tunnel. On the side 

 towards the mansion, the inclosed porch and roof of the entrance 

 to the tunnel being made in the construction of the grape-house, 

 cannot be considered a part of the cost of the former, but the flank- 

 ing walls, the steps, the tunnel itself, and the necessary covered 



