763 



PLATE VI. 



Fig. 7T. The proportions of the diameters of the 

 different parts of the double pullies being 3 to 2, 5 to 

 2, and 8 to 2, the middle weight may be observed to 

 rise the most rapidly. P. 88. 



Fig. 78. A wheel supposed to be capable of pro- 

 ducing a perpetual motion; the descending balls, act- 

 ing at a greater distance from the centre, but being 

 fewer in number, than the ascending. In the model, 

 the balls may be kept in their places by a plate of 

 glass covering the wheel. P. 92. 



Fig. 7^. A, the inclination of cross lines generally 

 most convenient for producing the effect of a tint, in 

 drawing, B shows the effect of lines crossing each 

 other perpendicularly, and C that of lines crossing too 

 obliquely. Where the surface to be shaded is large, 

 the separate lines or hatches should begin and end w ith 

 a point, in order that the junction of the different por- 

 tions may escape observation. P. 95. 



Fig. 80. Dr. Hooke's telegraph, in which the cha- 

 racters are arranged behind a screen, and drawn out 

 as they are required. P. 100. 



Fig. 81. Dr. Ilooke's alphabet, with some other 

 arbitrary characters for his telegraph. P. 100. 



Fig. 82. A beam compass, witli a scale. P. 102. 



Fig. 83 . . 85. Instruments for drawing arcs of 

 large circles. P. 102. 



Fig. 86. A pair of triangular compasses. P. 102. 



Fig, 87. Marquois's scales, for drawing parallel lines. 

 P. 103. 



Fig. 88. A pen for ruling musical lines. P. 103. 



Fig. 89. A pantograph. A being the centre of motion, 

 B the tracing point, and C the describing point, AB 

 is always to AC as A D to A E, and the copy F is si- 

 milar to tlie original G. P. 103. 



Fig. 90. A pair of proportioaal compasses. P. 104. 



