168 



USING MACHINES 



Can you trace the mechanical energy of the auto- 

 mobile back to the sun? 



In most instances the energy of the sun is utilized 

 by man indirectly through coal, gas, or falling water. 



Court c 



:n Institution 



FIG. 282. SOLAR COOKER 



However, there have been several attempts to harness 

 the sun's energy directly, and some of these have 

 been moderately successful. In Florida and California 



many persons have installed 

 water coils which supply 

 their homes with water heat- 

 ed by the sun's energy. 



One of the simplest and 

 most efficient devices ever 

 designed to harness the en- 

 ergy of the sun directly is 

 shown in Figure 282. It was 

 built by Dr. C. G. Abbott, di- 



j \w^ mxx rector of the Smithsonian In- 



\ \&. ^\X stitution. A cylindrical mir- 

 ror made from sheet alumi- 

 num collects the heat rays 

 from the sun and focuses 

 >s them on a small tube in the 

 center. This tube contains 

 some liquid such as oil or 

 water and is connected to a 



system of tubes through which the liquid may circu- 

 late as it becomes heated. The construction of the 

 tube is interesting. A blackened copper tube is placed 

 inside two glass tubes. The oil circulates inside the 

 copper tube. The photograph shows how Dr. Abbott 



FIG. 283. DIAGRAM OF 

 SOLAR COOKER 



has used this solar heater for purposes of cooking. 

 The drawing is a detail of the working parts. 



Exercise. Study the drawing of Figure 283 carefully 

 and note all the ways taken to get the greatest amount 

 of heat energy to the oven. Tell what scientific princi- 

 ple is made use of in each of the attempts to increase 

 the efficiency of the cooker. 



There are at least five types of energy : heat, light, 

 electrical, mechanical, and chemical. Some scientists 

 believe that matter itself is a sixth type. Many of the 

 common devices which we use every day are energy 

 transformers electric lights, heaters, and motors ; 

 coal and gas stoves ; dry cells and storage batteries. 

 In every case of transformation, some energy is 

 wasted, for there are no devices which are one hun- 

 dred per cent efficient. Can you name other devices 

 which we use to transform one type of energy into 

 another? 



REFERENCES FOR FURTHER STUDY 

 Texts 



Caldwell and Curtis, Science for Today, Chap. 8 



Clement, Collister, and Thurston, Our Surroundings, Chaps. 

 2, 6, 18 



Hunter and Whitman, Science in Our World of Progress, 

 Unit 8 ; Science in Our Social Life, Unit 8 



Lake, Harley, and Welton, Exploring the World of Science, 

 Chap. 18 



Pieper and Beauchamp, Everyday Problems in Science, Units 

 12, 13 



Powers, Neuner, and Bruner, Man's Control of His Environ- 

 ment, Chaps. 17, 18 



Stalling, Tours through the World of Science, Tours 8, 9 



Van Buskirk and Smith, The Science of Everyday Life, 

 Chap. 16 



Watkins and Bedell, General Science for Today, Unit 7 



Webb and Beauchamp, Science by Observation and Experi- 

 ment, Unit 5 



Wood and Carpenter, Our Environment: How We Use and 

 Control It, Topics 2, 3, 10, 11 



Special references 



Bond, The American Boys' Engineering Book 

 Bond, With the Men Who Do Things 

 Burns, The Story of Great Inventions 

 Darrow, Masters of Science and Invention 

 Marshall, The Story of Human Progress 



WHAT YOU SHOULD AIM TO ACQUIRE FROM 

 THIS STUDY 



1. An understanding of how the sun is the source of 

 all energy and the ability to trace all energy back 

 to it. 



2. An understanding of the law that energy can 

 neither be made nor be destroyed by man, but can 

 be changed from one of its forms into another. 



3. An understanding of the way in which the 

 following things work: electric heating devices, 

 steam engines and turbines, electric lights and 

 gas lights, water wheels and turbines, electric 

 motors and generators. 



