xvi DESCRIPTION OF PLATES. 



PLATE XIV. 



Fig. 178. Three sketches for wooden bridges ; the last requires no abutments. 

 P. 131. 



Fig. 179. The centering used for building one of the arches of Black Friars 

 Bridge. It was struck, or removed, by forcing back the compound wedges A, B, 

 by the impulse of a battering ram. P. 131. 



Fig. 180. Modes of supporting a series of rods, for communicating alternate 

 motion. A is the best and most common method, the rods being suspended from 

 a centre above them : at B the centre of motion is below the rods. Where 

 there is a declivity, the arrangement at C may be useful. The mode shown at D is 

 also recommended in some cases. P. 133. 



Fig. 181. A lever strengthened by a projecting frame. P. 133. 



Fig. 182. A bent lever strengthened by a cross bar. P. 133. 



Fig. 183. Hooke's universal joint. P. 133. 



Fig. 184. A wheel with a crank, for producing alternate motion in a rod. 

 P. 134, 257. 



Fig. 185. A wheel with an inclined and undulated surface, for producing alternate 

 motion in a rod, with the interposition of a friction wheel. P. 134, 257. 



Fig. 186. A frame for guiding the motion of a point A in a direction nearly rec- 

 tilinear, A B being to CD as C D to BE. [It is termed a parallel motion, Watt 

 obtained a patent for it on the 28th of April, 1784.] The dotted line shows the 

 path of the point A. P. 134, 257. 



Fig. 187. A frame for producing a motion nearly rectilinear in the point A. It 

 may be applied to a pump rod B C, worked by a crank, or otherwise. P. 134, 257. 



Fig. 188. A compound frame, for keeping two rods AB, C D, in a direction 

 very nearly parallel. E F is 36 parts of the scale, F G, 64, G H and H I each 80, 

 EH and H K 20, GL $ GK, or 106, KM 33, and LM and MN each 133. 

 P. 134. 



