246 



LIGHT IN THE HOME 





registered. Replacing the fishtail burner by a mantle and burner, 

 how does the light produced in the two cases compare? How much 

 gas is being consumed in the latter case ? What is your conclusion ? 

 (If a Thorp gauge is not available, test the gas consumed in a specified 

 time by observing the small indicator of the gas meter dial.) 



The first electric lamp. It is due Jto Thomas Edison 

 that we have the incandescent light. The story of its 

 invention is well known. He worked for a great many 

 years and spent hundreds of thousands of dollars in the 



perfection of the bulb light, 

 patented in 1880, which he 

 furnished finally with a car- 

 bon filament, made of bam- 

 boo. The way in which 

 this filament gives light can 

 be explained better after we 

 have performed an experi- 

 ment to illustrate what 

 makes electricity give light. 

 Electricity is a form of 

 energy which is conducted 

 easily by metals. We have 

 all seen that the pipe con- 

 ducting liquids in the house offers resistance to them so that 

 they do not flow so easily. In somewhat the same way 

 wires offer resistance to electricity. That part of the elec- 

 trical energy used in overcoming this resistance to the wire 

 conductor is changed into heat, which when intense enough 

 produces light. This may be shown by the following ex- 

 periment : 



Experiment. To show how electricity may be changed into light. (To be 

 performed by the teacher.) 



The carbon filament incandescent lamp and 

 the modern tungsten lamp. 



