APPARATUS FOK EXPERIMENTS. 283 



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

 roads, by usiuj; 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. 231, p. 204, may be rendered easy and inter- 

 esting by purchasing a large and perfectly-working syringe^ and attach- 

 ing 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 pis- 

 ton 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 prin- 

 ciple. 



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. 212. 

 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. 236, 237, and the difference in time for emptying the ves- 

 sel 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 bloAving with the mouth into one end. 



25. Any vessel, filled with sand which has been heated over a fire, 

 with rods of different substances, nearly of an equal size and length, 

 and thrust with one end into the hot sand, in an inclined or nearly hori- 

 zontal position, will exhibit the various conducting powers of these 

 rods by melting pieces of wax or tallow i)laced on the ends most remote 

 from the sand. 



26. The expansion by heat may be demonstrated by fitting an iron 

 rod to a hole in sheet-iron ; on heating the bar it can not be made to 

 enter. Or, if a hot iron ring be slipped on a tapering cold iron rod, it 

 will contract on cooling so that the force of a man can not withdraw the 

 rod. 



27. The rising and descending currents in a vessel of heating water 

 are easily rendered visible by throwing into a glass vessel, or flask, over 

 a lamp, particles of sawdust from any hard, green wood, Avhose specific 

 gravity is about the same as that of water. 



28. Instrument figured on p. 265, for showing the principle of the 

 Bteam-engine. 



29. Experiments in latent heat may be easily exhibited with the as- 

 sistance of a common thermometer. 



30. Tin mirrors for showing radiation, p. 278. 



