WALLS, ESPALIER-RAILS, AND TRELLIS-WORK. 



181 



glass, and as heightening architectural effect. Walls are almost always 

 built perpendicularly to the horizon, but they have been tried at different 

 degrees of inclination to it, in order to receive the sun's rays at right angles 

 when he is highest in the firmament during summer ; but though some 

 advantage may probably have been obtained from such walls at that season, 

 yet the great loss of heat by radiation during spring and autumn would 

 probably be found greatly to overbalance the gain during summer. Nicol 

 informs us that he constructed many hundred feet of boarded walls which 

 reclined considerably towards the north, in order to present a better angle to 

 the sun, but he does not inform us of the result ; a German gardener, how- 

 ever, has found advantage from them. (See Nicol' s Kal. p. 149, and Hort. 

 Trans, vol. iv. p. 140.) 



473. Treliised walls. — Where the surface of a garden wall is too rough, 

 or is formed of too large stones to admit of conveniently attaching the 

 branches of trees to it, by nails and shreds, it becomes necessary to fix to the 

 wall trellis- work of wood or of wire. The laths or wires are generally placed 

 perpendicularly six or eight inches apart, because the branches are generally 

 trained horizontally, or at some angle between horizontal and perpendicular. 

 Wires stretched horizontally, however, and screwed tight, form the most 

 economical description of trellis; and if occasionally painted, they will last 

 a number of years. Trellis-work of wood is more architectural, and the 

 branches are more readily fixed to them by ties, which are apt to slide along 

 the small wire unless the double operation is performed of first attaching the 

 tie to the wire, and then tying it to the shoot of the tree. The colour both 

 of the wire and the woodwork should not differ much from that of the stone 

 of the wall, otherwise it will become too conspicuous. 



474. Colouring the surface of walls blacky with a view to the absorption 

 of heat, has been tried by a number of persons, and by some it has been con- 

 sidered beneficial ; but as the radiation during night and in cloudy weather 

 is necessarily in proportion to the absorption during sunshine, the one ope- 

 ration neutralizes the other. If, indeed, we could insure a powerful absorp- 

 tion from a bright sun during the day, and retain the radiation by a canvass 

 or other screen during the night, a considerable increase of temperature 

 might probably be the result ; but the number of cloudy days in our climate 

 in proportion to those of bright sunshine is not favourable to such an ex- 

 periment. 



475. Flued walls are either built entirely of brick, or with one side of 

 brick and the other of stone ; the latter being the north side of east and 

 west walls. In the case of north and south walls which are to be flued, the 

 thickness is equal on both sides, and the wall is built entirely of brick. The 

 flues, Avhich are generally from six to eight inches wide, commence about one 

 foot above the surface of the border ; the first course is from two to three 

 feet high, and each successive course is a few inches lower, till the last flue, 

 within a foot of the coping, is about eighteen inches high. The thickness 

 of that side of the flue next the south should, for the first course, be four 

 inches, or the width of a brick laid flatways ; and for the other courses it is 

 desirable to have the bricks somewhat narrower, on account of the heat being 

 less powerful as the smoke ascends. All the bricks, however, whatever may 

 be their width, must be of the same thickness, in order to preserve uniformity 

 in the external appearance of the w^all. As where garden walls are to be 

 built a large supply of bricks is requisite, no difficulty need occur in getting 



