164 



USING MACHINES 



the spark plug and the other so that it touches some part of 

 the can. Now spray a little gasoline into the can with an 

 atomizer or Flit spray. Place the lid on securely and close 

 the switch. Stand away from the can and be cautious as 

 the switch is closed. In your notebook record the notes of 

 this experiment. Write a summary paragraph explaining 

 your results and pointing out how this set-up is modified in 

 the gasoline engine. 



Experiment 116. How can the horse power of one's 

 body be determined? 



The horse power is a unit for measuring the rate at which 

 a machine can do work. One horse power is work done at 

 the rate of 33,000 foot pounds per minute or 550 foot pounds 

 per second. Locate a straight flight of stairs from ten to 

 fifteen feet high. Measure the height of one step in feet and 

 multiply this by the number of steps. This will give the exact 

 height of the stairs. Determine the time in seconds that it 

 takes you to run to the top. Your weight multiplied by the 

 height of the stairs in feet will give the foot pounds of 

 work done. Divide this by the number of seconds it takes 

 you to reach the top and it will give the number of foot 

 pounds of work done per second. If this is again divided by 

 550 it will give the horse power of your body. Try several 

 times and record your data in your notebook. 



READINGS WHICH WILL HELP ANSWER 

 THE PROBLEM QUESTIONS 



How is the energy of coal harnessed and controlled? 



Our homes are heated and lighted by energy which 

 comes from coal, oil, gas, or water power. Automo- 

 biles, airplanes, locomo- 

 tives, and ships are all 

 driven by energy derived 

 from coal or oil. Rapid 

 communication is made 

 possible only by electric- 

 ity, which may also come 

 from any of the natural 

 sources named above. In- 

 dustry would not long 

 continue if our natural 

 supplies of energy were 

 suddenly cut off. Think 

 what a calamity would re- 

 sult. Man has harnessed 

 the power of most of the 

 natural sources of energy 



FIG. 270. HERO'S BALL 

 OF THE WINDS 



including coal, oil, gas, 



water power, wind power, and to a small extent the 

 power of the tides. Recently Claude, a French scien- 

 tist, attempted to harness the heat energy of warm 

 ocean waters, but found the process too difficult for 

 general use. 



As long ago as 130 B.C. man began experimenting 

 with the power of steam. About that time a man by 

 the name of Hero, who lived in the city of Alexandria, 

 Egypt, made what he called a "ball of the winds." He 

 had a globe with a pair of hollow bent arms extending 



FIG. 271. PORTA'S ENGINE 



from it in opposite directions as shown in Figure 270. 

 The globe was partly filled with water and a fire built 

 under it. As steam issued from the bent arms and 

 pushed against the air, the globe turned much as a 

 whirling lawn sprinkler turns when water pushes 

 against the air as it comes out of the tiny openings. 

 The ball of the winds was only a toy, but it was the 

 probable beginning of our modern steam turbine. 



In 1601 Porta, an Italian, built a type of engine in 

 which he used the expansive power of steam to do 



work. Steam was gener- 



ated from water in a boil- 

 er and forced to the top of 

 a second chamber partly 

 filled with water. Another 

 pipe led from the water 

 chamber to a higher level. 

 As the steam expanded it 

 pushed on the surface of 

 the water with sufficient 

 force to raise some of it 

 to a higher level. Figure 

 271 shows how Porta's 

 original engine appeared. 

 In 1629 another Italian by 

 the name of Branca built 

 an engine run by steam which in some ways closely 

 resembles a modern steam turbine. A jet of steam was 

 blown against the blades of a specially constructed 

 wheel, causing it to turn. It is said that this engine 

 was used by Branca for pounding drugs and other 

 chemicals. Figure 272 is a drawing of Branca's engine. 



One of the greatest steps forward in harnessing the 

 energy of coal by means of the steam engine came in 

 the discovery of the cylinder and piston by Denis 

 Papin, a Frenchman. The piston moves inside the cyl- 

 inder as shown in Figure 

 277. The piston is used in 

 modern steam, gas, and oil 

 engines. 



The first steam engine 

 to make use of the piston 

 was built in 1705 by an 

 Englishman named New- 

 comen. In reality it was 

 not a steam engine (in the FIa 272 ' BRANCA ' S ENGINE 

 modern sense), but an air pressure engine. A study 

 of Figure 273 will show that Newcomen's engine op- 

 erated a lever beam, to one side of which was attached 

 a heavy counter balance weight. Steam from the boiler 

 was first admitted to the cylinder and then cut off by 

 closing a valve. Cold water was then sprayed into the 

 cylinder. This condensed the steam and decreased 

 the pressure inside the cylinder. The greater air pres- 

 sure on the outside then pushed the piston down, 



