774 



PLATE XVII. 



Fig. 213, A jack for laisiag welglits by the alter- 

 nate motions of a lever, the clicks on each side being 

 detained in the teeth of the ratchets by the assistance 

 of the springs in which they terminate, and which are 

 coiinccied together. P. 204. 



Fig. 214. The mode of supporting a tackle for 

 raising stones in building ; the summit of the triangle, 

 which is composed of three poles, being raised or 

 lowered by means of a rope and puUies. P. 907. 



Fig. ai5. A method of raising weights obliquely, 

 by means of a rope, passing over a pulley, which is 

 drawn along horizontally. P. 207. 



Fig. 216. AB, a section of an inclined plane, belong- 

 ing to the Duke of Bridgwater's canal: the boats are 

 drawn into the looks at A, which are then filled with 

 water ; C is the plan of the windlass, by which the de- 

 scending and ascending boats are connected together, 

 and which is turned by a winch ; D and E a"re the 

 locks. P. 308. 



Fig. 217. A crane, with an oblique walking wheel, 

 for oxen or horses. The wheel is taken from a mill 

 of Leupold. P. 209. 



Fig. 218. A crane with a wheel and break like Mr. 

 White's. The man wdlks at any required distance 

 from the axis of motion, and pushes forwards the lever 



A, which moves the bar B C, connected to the same 

 axis, and removes the break CD from the ciicuiiife- 

 rence of the wliccl. P. 210. 



Fig. 219. A lewis, for raising stones. P. 210. 

 Fig. 220. When the centre of gravity A is twice as 

 far from one of the porters B, as from the other C, the 

 first bears one third of the weight, the other two thirds. 

 P. 212. 



Fig. 221. When the centre of gravity A is above the 

 line joining the points of support B, C, the load is di- 

 vided in the ratio of the segments CD, BD, termi- 

 nated by the vertical line AD; but it may be sup- 

 ported by two equal forces in the directions BE, C F, 

 found by makhig G H equal to BG, and joining C H; 

 the angle G B E being equal to G U F; the forces and 

 the weight may then be rtpreseutcd by the lines C I, 

 IK, andCK. P. 212. 



Fig. 222. A roller with two wheels fixed on its ends, 

 by means of which tlie slab resting on it may be 

 moved to a considerable distance without leaving the 

 roller behind. P. 213. 



Fig. 223. Mr. Garnet's roIlers,for diminishing fric- 

 tion : their axes being loosely connected by a ring, in 

 order to keep tliem in their places. P. 213. 



