350 



SCIENCE OF GARDENING. 



Part II. 



1 lIlS 





307 308 309 310 



Ireland, the Highlands of Scotland, and Lapland. 

 Modifications of this and other rude forms (Jigs. 307. 

 to 310.) may sometimes be admitted in garden-scenery, 

 as tool-houses, or shelters for other materials, game, 

 &c. — A variety of examples of rustic huts and 

 cottages are to be found in Kraft's plans, &c. ; and of 

 highly decorated cottages and ornamented buildings 

 in Mrs. Hofland's White Knights, and Ackermann's 

 Repository of the Arts. 



1782. The bridge is one of the grandest decorations 

 of garden-scenery, where really useful. None require 

 so little architectural elaboration, because every mind 

 recognises the object in view, and most minds are 

 pleased with the means employed to attain that object 

 in proportion to their simplicity. There are an im- 

 mense variety of bridges, which may be classed accord- 

 ing to the mechanical principles of their structure ; 

 the style of architecture, or the materials used. 



With respect to the principles of their mechanical structure, the materials of bridges are held together, either 

 by their gravity, as in all arches, whether of stone, iron, or timber ; or by their tenacity, as in single planks, 

 flat bridges of iron or timber, and those new and wonderful exertions of ingenuity, suspended bridges, of 

 which fine examples have been executed across the Menai and the Tweed, and the principles of which we 

 have elsewhere (Annals of Philosophy, Jan. 1816-) entered into at large. 



With respect to styles of architecture, the bridge affords little opportunity of detailed display ; but the 

 openings may be circular or pointed arches, or right-lined, or a mixture of these. 



As to material, bridges of tenacity are formed of timber or wrought-iron ; bridges of gravity, generally 

 of cast-iron or stone ; but they may be formed of any material. We submit a few examples in different 

 styles, and composed of different materials. 



1783. The fallen tree is the original form, and may sometimes be admitted in garden- 

 scenery, with such additions as will render it safe, and somewhat commodious. 



1784. The foot-plank is the next form, and may or may not be supported in the middle, 

 or at different distances by posts. 



1785. The Swiss bridge (Jigs. 312, 313.) is a rude composition of trees unbarked, 

 and not hewn or polished. 



312 



311 



1786. The tied plank {fig. 314.) is formed by fixing the ends of one or more planks 

 in two heads or cases of cast-iron (a, a), and then connecting them by wrought-iron 

 rods (b, b) fixed to the heads in the manner of a string to a bow. A very light bridge 

 is thus formed, which acts both by tenacity and gravity. Thus, when a light weight 

 is on the bridge, the particles of the boards are not moved, but merely pressed on, and 

 therefore the arched part may then be said to act by gravity ; while this pressure being 

 propagated to the abutments, these are held in equilibrium by the iron rods acting by 

 their tenacity. On the other hand, when a bridge of this sort is heavily loaded, the 



