470 NATURE-STUDY 



saw?* What is a balance, crowbar, pitchfork, fish-pole, 

 etc ? Do not try to apply the law of the lever, or refer to the 

 three kinds of levers. Similarly study in a simple, exper- 

 imental way simple pulley,* block and tackle, gearing, 

 belts,* derrick.* Note particular advantages gained from 

 each. (251, 250, 255, 257, 217, 318.) 



Forces of nature man has learned to utilize : Begin with 

 primitive man. Note absence of tools and labor-saving 

 machines. To-day we use the forces of animals, the wind, 

 water-power, steam, and electricity. Let children mention 

 illustrations.* Visit places showing application of these 

 forces. Visit a factory. What runs all the machines? 

 (References as the last.) 



Heating house by furnace — apply convection.* Hot- 

 water heating. Apply convection. Illustrate by exper- 

 iments.* (References like the last.) The kitchen hot-water 

 tank. 



City water supply:* Source. Pumping station, or reservoir, 

 mains, water pressure (simple). (References like the last.) 



Chemistry: Simple experiments to make and show 

 the properties of oxygen, nitrogen, and carbon dioxide. Show 

 in the air, or make from the air. Combustion chemistry 

 (very simple), oxygen of air uniting with carbon (charcoal) 

 to make carbon dioxide. Effects of CO^ on a flame, on life. 

 Test in air with lime-water. Test the breath with lime- 

 water. CO2 in breath. Connect with physiology. (262, 

 263, 264, 267, 269, 270, 272.) 



Natural waters: See earth study above. Ocean-water, 

 why salt ? How table-salt is made from sea water, and why 

 it is found in the earth. (262, 263, 264, 317, 318, 326, 327, 

 328.) 



