UNIT V. HOW WE 



The brilliant illumination found today in our 

 homes, public buildings, and city streets has been 

 made possible through recent rapid advances in the 

 fields of science and invention. The great improve- 

 ment from the smoky pine torch and candles of early 

 times to the brilliance of our present day electric lamp 

 is a remarkable example of the progress oi science 

 and invention. Early dwellers on the earth had no 

 other light than that received from the sun during 

 the day and the moon and stars by night. The dark- 

 ness was feared and man's activity practically ceased 

 at sunset. 



The bonfire was probably the first form of artifi- 

 cial light used by early man, but when and how he 

 learned to use it we shall probably never know. Next 

 came the development of the pine torch, by means of 

 which our ancestors were able to leave their dwelling 

 places at night. The use of the pine torch persisted 

 for many centuries, but as civilization progressed 

 various new devices were tried. Dried rushes boiled 

 in grease from cooked meats were used for a while 

 and were soon followed by bowls of grease in which 

 some form of wick was placed. Then the candle, made 

 from solid fats and waxes, was invented, its efficiency 

 being so much greater than that of any of the preced- 

 ing devices that it remained the chief source of arti- 

 ficial light for centuries. The candle was eventually 

 replaced by the kerosene lamp, which has since been 

 replaced by our modern gas and electric lights. 



The invention of window glass, about four hundred 

 years ago, combined with our modern gas and elec- 



LIGHT OUR HOMES 



trie lighting systems, has made our homes cheery 

 places in which to live both by day and by night. 

 During the Middle Ages the castles of the wealthy 

 noblemen were just as dark and damp as the tiny 

 huts of the peasants, for there was no way of letting 

 in the light and at the same time keeping out the cold. 

 In this unit you will learn some of the fundamental 

 principles of light, the methods of producing artificial 

 light, and principles of control of the illumination in 

 your homes in a hygienic way. You will also learn 

 about devices which make use of light, such as the 

 human eye and the camera. 



How many of these questions about light can you 

 answer? Write the answers in your notebook under 

 the proper heading. 



1. What is light? 



2. How does light from the sun reach the earth? 



3. How many devices for producing artificial light 

 have you in your own home? 



4. Which do you find the more cheerful in your 

 home, rooms with light-colored walls or rooms with 

 dark-colored walls? Why? 



5. What causes an electric-light bulb to give light ? 



6. What are the colors of a rainbow? What causes 

 a rainbow? 



7. Name ways by which we derive benefit from 

 light. 



8. Why are you able to see yourself in a mirror? 



9. Why is the flame of a lighted candle yellow? 



10. Who invented the incandescent bulb? 



TOPIC 1. THE HISTORY OF LIGHTING 



SUGGESTED PROBLEMS AND QUESTIONS 



1. How did people of olden times light their 

 homes? 



2. What happens in a candle, a kerosene lamp, 

 and a gasoline lamp when they produce light? 



3. How is gas used for producing light? 



4. How is an electric-light bulb constructed? 



5. How is electricity used for lighting? 



SUGGESTIONS AND HELPS FOR STUDY 



1. Problem 1 is a historical question which will re- 

 quire considerable reading from special references. 



2. You can find some material for problems 2, 3, 

 4, and 5 by examining and experimenting with vari- 

 ous lighting devices in your own home. 



3. In connection with problem 4, secure an electric 

 light bulb at home or from your teacher and see how 

 the electricity enters and passes through the bulb. 



4. You may find the following new words in this 

 study: 



capillarity the cause of the rising of liquids in small 

 tubes. 



luminous giving light. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS 



Experiment 66. What happens when a candle burns? 



Light a large candle. When you look at the flame closely 

 you will probably be able to see that it is made up of three 

 zones. What is the color of each zone? 



Hold a wooden splint across the 

 flame a short distance above the 

 wick. Remove it as soon as it catches 

 fire and extinguish the flame quickly. 

 Is all of the wooden splint that was 

 in the flame burned? Which zone of 

 the flame is the hottest? Which is 

 the coolest? 



Hold a dry, cold, clean pint jar 

 over the candle flame for one min- 

 ute with the opening of the jar about 

 two inches from the flame. Examine 

 the jar. What has collected on it? 



Repeat the experiment with the jar. Put a small amount 

 of clear limewater into the jar. Coyer it and shake well. 



FIG. 140 



98 



