CONTENTS. xv 



effect of machines ; Experiments, 67. Cautions with regard to the construction 

 of machines, 68. Comparison of animal with inanimate force; Regulation of 

 force ; Small momentum of machines, 69. Impossibility of a perpetual 

 motion, 70. 



LECTURE X. 

 ON DRAWING, WRITING, AND MEASURING, 71. 



Subjects preliminary to the consideration of practical mechanics ; Instrumental 

 geometry; Statics; Passive strength ; Friction; Drawing; Outline, 71. Pen; 

 Pencil ; Chalks ; Crayons, 72. Indian ink ; Water colours ; Body colours ; 

 Miniatures ; Distemper ; Fresco ; Oil, 73. Encaustic paintings ; Enamel ; 

 Mosaic work ; Writing, 74-. Materials for writing ; Pens, 75. Inks ; Use of 

 coloured inks for denoting numbers ; Polygraph ; Telegraph, 76. Geo- 

 metrical instruments ; Rulers ; Compasses, 77. Flexible rulers ; Squares ; Tri- 

 angular compasses ; Parallel rulers ; Marquois's scales, 78. Pantograph ; 

 Proportional compasses; Sector, 79. Measurement of angles; Theodolites; 

 Quadrants ; Dividing engine, 80. Vernier ; Levelling ; Sines of angles, 81 . 

 Gunter's Scale ; Nicholson's circle ; Dendrometer ; Arithmetical machines ; 

 Standard measures, 82. Quotation from Laplace ; New measures ; Decimal 

 divisions ; Length of the pendulum, and of the meridian of the earth, 83. Mea- 

 sures of time, 84. Objections ; Comparison of measures, 85. Instruments for 

 measuring ; Micrometrical scales ; Log lines, 86. 



LECTURE XI. 



ON MODELLING, PERSPECTIVE, ENGRAVING, AND PRINTING, 87. 



Copying a statue ; Modelling; Casting, 87. Perspective; Mechanical perspec- 

 tive ; Geometrical perspective, 88. Orthographical projection, 89. Projections of a 

 sphere, 90. Invention of engraving ; Wood cuts ; Mode of engraving ; Ruling, 91 . 

 Me/zotinto; Etching, 92. Aquatinta; Musical characters ; Printing; Copying 

 letters ; Printing from stones, 93. Letterpress ; Stereotype printing, 94-. 



LECTURE XII. 

 ON STATICS, 95. 



Weighing ; English and French weights, 95, 96. Balances, 96. False balances ; 

 Weighing machines ; Steelyards, 97 ; Bent lever balances ; Spring steelyard ; 

 Dynamometer ; Animal actions ; Strength of muscles, 98. Instances of strength, 

 99. Progressive motion ; Running, 100. Pulling ; Sources of motion ; Work 

 of a labouring man, 101. Temporary exertions ; Horses, 102. Wind; Water; 

 Steam; Gunpowder; Measurement of small forces, 103,104-. 



LECTURE XIII. 



ON PASSIVE STRENGTH AND FRICTION, 104. 



Immediate effects of force on a solid ; Extension and compression ; Rigidity, 

 105. Measure of elasticity, 106. Detrusion; Lateral adhesion; Flexure, 107. 

 Cause of irregularities; stiffness; Stiffness of beams; Hollow beams; Torsion, 

 108. Alteration ; Ductility, 109. Temper of metals ; Toughness ; Brittleness ; 



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