DESCRIPTION OF PLATES. 



PLATE IV. 



Fig. 51. The weight A, acting on the double cylinder B, supports the weight C 

 by the pulley running in the angle of the rope D C E, which is wound on the larger 

 cylinder at D, while it is uncoiled from the smaller at E, and the force is the same as 

 if the weight C were attached to the line C F, acting on the axis F, of which the 

 diameter is equal to the difference of the radii of the double cylinder. P. 52, 158. 



Fig. 52. A single fixed pulley, supporting two equal weights. P. 52. 



Fig. 53. A single moveable pulley, by means of which a weight supports another 

 twice as great. P. 52. 



Fig. 54. The arrangement of pullies in ships' tackles, with a force of six to one. 

 P. 53. 



Fig. 55. An arrangement of pullies in a vertical line, with a force of six to one. 

 P. 53. 



Fig. 56. Mr. Smeaton's blocks, giving a force of twenty to one, the rope being 

 applied in the middle of the outer series, and following the order of the figures from 

 1 to 21. P. 53, 159. 



Fig. 57. A system of pullies fixed on one axis hi each block ; having a power of 

 8 to 1. P. 53. 



Fig. 58. A system of pullies, each of which doubles the effect ; having a power of 

 8 to 1. P. 53. 



Fig. 59. A system of pullies with each rope fixed to the weight, having a force of 

 7 to 1. P. 53. 



Fig. 60. Two systems of pullies, of the kind denominated Spanish bartons, in 

 which two of the pullies are suspended by the same rope ; the one has a power of 4, 

 the other of 5. P. 53. 



Fig. 61. A. The depression of the middle weight being one third of its distance 

 from the pullies, it sustains two equal weights, which are together three times as 

 great as itself. B. The depression of the smaller weight being one fourth of its 

 distance from the pulley, it supports a weight twice as great as itself. P. 53. 



Fig. 62. A joiner's saw, stretched by twisting a double cord, by means of a lever 

 passing through it. P. 54. 



Fig. 63. The weight A, resting on an inclined plane of which the height is to the 

 oblique length as 3 to 5, is sustained by a weight B three fifths as great as itself; and 

 if for the resistance of the plane we substitute the action of the weight C, reduced to 

 the direction A D perpendicular to the plane, this weight must be four fifths of the 

 weight A, the horizontal length of the wedge being four fifths of its oblique length. 

 P. 54. 



Fig. 64. The weights A, B, and C, acting, by means of threads passing over 

 pullies, which are fixed to any required part of a horizontal table, on the rollers which 

 press against the sides of a wedge, proportional in length to the respective weights, 

 retain each other in equilibrium, when their directions meet in one point. In order 

 that the threads may pass on each side of the wedge, it may be supported by three or 

 more balls. P. 54. 



