APPENDIX. 261 



14. A lecturer may quickly demonstrate before a class the small in- 

 crease in the length of a road, in consequence of a considerable cun'e 

 to one side of a straight line (as shown by Fig. 70), by using a cord 

 for measuring, the diagram being marked on a board or the wall. 



15. A round stick of wood, and a long, wedge-shaped slip of paper, 

 easily show the principle of Fig. 75, p. 94. 



16. A cog-wheel with endless screw and winch, Fig. 77, p. 95, ex- 

 hibits distinctly the great power of the screw in this combination. 



17. Pine sticks, two feet long, and one fourth to one half inch 

 through, of different shapes and sizes, supported at each end, and with 

 weights hung at the middle till they break, may be made to illustrate 

 the principles described on p. 100, 102. 



18. Some of the principles of draught may be shown, and especially 

 those in relation to the different angles of inclination for hard and soft 

 roads, by using a common spring-balance as a dynamometer, attached 

 to a hand-wagon, and also to a sliding block of wood. 



19. Bent glass tubes, with arms of different sizes to indicate the up- 

 ward pressure of liquids, may be procured cheaply at glass-works. The 

 experiment described by Fig. 154, p. 182, may be rendered easy and 

 interesting by purchasing a large and perfectly-working syringe, and 

 attaching to its nose, by means of sealing wax, a slender glass tube 

 two or three feet long. Fill the syringe with water, leaving the 

 tube empty ; then, with the tube upright, drive the water up through 

 it with the piston of the syringe, and the increased weight felt on the 

 piston as the column of water rises will be very evident. 



20. A hydrostatic bellows a foot in diameter, made by any good 

 mechanic, will answer the purpose well, and exhibit an important 

 principle. 



21. Specific gravities may be shown before a class by a common 

 balance and a fine cotton or silk thread. 



22. A tin pail, with a hole half an inch or an inch in diameter at the 

 bottom, will show the contracted stream which pours from it, p. 191. 

 A short tin tube, with a slight flange at the upper end (quickly made 

 by any tin-worker), fitted into this hole, will increase the discharge, as 

 shown by Figs. 159, 160, and the difference in time for emptying the 

 vessel may be measured by a stop-watch. 



23. Archimedes' screw is readily made by winding a lead pipe round 

 a wooden cylinder. 



24. A glass syphon, filled with cochineal water, shows distinctly the 

 theory of waves, by blowuig with the mouth into one end. 



