xvi CONTENTS. 



Fracture; Strength; Resilience, 110. Effect of velocity; Limit of strength 

 or resilience, 111. Qualities of natural bodies; Fracture by simple com- 

 pression; Strength of lateral adhesion, 112. Transverse force; Fracture 

 by flexure, 113. Comparative strength and resilience, 113, 114. Uses of 

 resistances of different kinds ; Coach springs ; Comparison of direct and trans- 

 verse strength, 114. Beam cut out of a tree; Hollow masts; Strongest forms of 

 beams, 115. Machine for measuring strength; Strength of different substances, 



116. Inconvenience of bulk ; Friction; Lateral adhesion ; Uniformity of friction, 



117. Usual magnitude of friction, 118. Best direction for draught; Stability 

 of a wedge or nail, 119. Resistance to penetration, 120. 



LECTURE XIV. 

 ON ARCHITECTURE AND CARPENTRY, 121. 



Architecture; Form of a column, 121. Eddystone lighthouse; Wall, 122. 

 Joints; Mortar; Arch, 123. Oblique pressure of earth, 124. Bridge; Flat arch, 

 125. Horizontal thrust; Piers; Blackfriars bridge; Dome, 126. St. Paul's 

 cathedral; Pantheon; Orders of architecture ; Gothic architecture, 127. Carpen- 

 try; Joints, 128. Scarfing ; Joggles ; Tenons ; Mortises ; Straps, 129. Inconve- 

 nience of transverse strains ; Roofs ; Kirb roof; Height of a roof, 130. Wooden 

 bridges; Centres of bridges ; Furniture; Parker's gates, 131. 



LECTURE XV. 

 ON MACHINERY, 132. 



Application of force, 132. Levers; Connected rods; Hooke's joint; Cranks, 

 133. Winches; Rectification of circular motion; Wheel work, 134. Teeth of 

 wheels, 135. Kinds of wheels, 136. Eccentric wheels; Sun and planet wheels; 

 Construction of wheels ; Weights and springs ; Fly wheels, 137. Air vessels, 138. 



LECTURE XVI. 

 ON THE UNION OF FLEXIBLE FIBRES, 138. 



Chain; Union by means of adhesion; Friction of a rope on a cylinder; Twist- 

 ing; Spinning; Rope-making, 139. Materials of ropes; Hemp, 140; Flax; 

 Cotton, 141. Silk; Wool; Weaving, 142. Crape; Cloth; Felts; Hats, 143. 

 Paper, 144. 



LECTURE XVII. 

 ON TIMEKEEPERS, 144. 



Clepsydrae, 144. Clocks ; Fly clocks, 145. Balances ; Chronometer with a 

 revolving pendulum, 146. Measurement of minute intervals of time; Pendulum ; 

 Balance spring; Principal requisites of a timekeeper; Sustaining force, 147. 

 Equalization of the force ; Intermediate spring or wheel; Scapement ; Crank, 148. 

 Crutch scapement ; Common watch scapement, 149. Dead beat scapement and 

 horizontal watch ; Friction of scapements ; Duplex scapement ; Common scape- 

 ment; Scapements of Harrison, Mudge, 150. Scapements of Haley, Camming, 

 Nicholson, Arnold, and Earnshaw; Isochronism of vibrations, 151. Properties of 



