358 



SCIENCE OF GARDENING. 



Part II, 



1822. Of constructions for diq)laymg water, as an artificial decoration, the principal are 

 cascades, waterfalls, jets, and fountains. The foundation of the cascade and waterfall, is 

 the head or dam which must be thrown across the river or stream ; and in this, two things 

 are to be considered, its strength, and the materials of which it is composed. 



1823. JFith respect to strength, the pressure of water is as its depth, and consequently a 

 dam, whose section is a right-angled triangle {fig- 340. a, b, c), and whose hypothenuse 

 (a, b) forms an angle of 45°, 'with the base (a, c) formed of any material of greater specific 

 gravity than water, would, as far as strength is concerned, hold in equilibrium a body of 

 still water of a depth equal to its perpendicular. If the hypothenuse, or sloping side, 

 be placed next the water, it will more than hold the water in equilibrium, by the weight 

 of the triangle (a, b, d) of the water superincumbent on the triangle of the dam or bank. 



1824. That the materials of the bank must be of a nature impervious to water, and also 

 must adhere to the base or bottom, so as not to admit water to escape beneath it, are ob- 

 vious conditions of the foregoing proportion. The practice of forming dams or heads, is 

 derived from this theory ; but to guard against accident, the base of the triangle is always 

 made three or more times greater than its height ; the slope next the stream may form an 

 angle with the horizon, of from 40° to 20°, and that on the lower side is regulated by the 

 uses of the dam. If for raising water so as to cover a hollow where there is little or no 

 overflow expected, then the slope is generally of earth, 40° or 35° {fg' 340. e,f), turfed 

 or planted ; if for a cascade, the slope is regulated by the form or undulations on which 

 the rocks to produce the breaking of the water are to be placed ; and if for a waterfall, a 

 perpendicular wall is substituted, over which the water projects itself in a sheet or lamina, 

 in breadth proportioned to the quantity of the current. 



1 825. In all these cases, instead of forming the dam entirely of materials impervious 

 to water, it is sufficient if a vertical stratum of wrought-clay be brought up its centre 

 {fg. 340^ g'.f), and the surface of the bank rendered firm by a coating of gravel on the 

 slope next the water. 



1826. The construction of the waterfall, where avowedly artificial, is nothing more than a 

 strong-built wall across the stream, perfectly level at top, and vnih a strong, smooth, ac- 

 curately fitted, and well jointed coping. On the perfection of the coping, both as to level 

 and jointing, depends the regular distribution of the lamina of water to be projected. 

 Formerly artificial cascades of this sort Avere curved in the grourxd-plan, the concavity 

 pointing down the stream, by which some strength and a better view of the water were 

 supposed to be obtained. With respect to strength, ibis can only hold true, or at least be 

 of consequence, in cases where the upper slope of the dam is very steep, and the force of 

 the current great ; and as to a fuller view, this can only take place when the eye of the 

 spectator is in the focus of the segment. Where a natural waterfall is to be imitated, the 

 upright wall must be built of huge irregular blocks ; the horizontal lamina of water 

 broken in the same way by placing fragments of rocks grouped here and there so as -to 

 throw the whole into parts ; and as nature is never methodical, to form it as if in part a 

 cascade. 



1827. In imitating a -natural cascade in garden-scenery, the horizontal line must here 

 also be perfect, to prevent waste of water in dry seasons, and from this to the base of the 

 lower slope the surface must be paved by irregular blocks, observing to group the promi- 

 nent fragments, and not distribute them regularly over the surface. In the infancy of 

 landscape-gardening, the lower bank or slope of the dam was formed into ogee and other 

 curves, or a serpentine line, and smoothly paved or causeyed, fixing on the convexities of 

 the curves projecting boards across the current ; and the current being thus interrupted, 

 was thrown up in arched waves. Such was the sort of beauty then admired; for it is a 

 long time in the progress of improvement before man can see any other beauty than tliat 

 which he has himself produced. 



1 828. The greatest danger in imitating cascades and waterfalls, consisting in attempting 

 too much, a very few blocks, disposed with a painter's eye, will effect all ♦•hat can be 

 in good taste in most garden-scenes ; and in forming or improving them in natural 

 rivers, there will generally be found indications both as to situation and style, especially 

 if the country be uneven, or stony, or rocky. Nothing can be in worse taste than piles of 

 stones and rocks across a river either natural or artificial, in a tame alluvial meadow : they 

 may be well chosen fragments from suitable materials, and arranged so as to form a cas- 

 cade or waterfall very beautiful of itself, but whose beauty is really deformity or mon- 



