Y 



244 GENERAL SCIENCE 



Acetylene. -- The gas is made by the action of calcium 

 carbide and water. When thoroughly mixed with air 



(Figure 220), it burns 

 with a smokeless flame 

 of brilliant whiteness. 



Electric Lighting. - 

 The most common method 

 of lighting in cities at 

 -*- the present time is by 



FIG. 220. An Acetylene Burner and electricity, Using the hl- 



candescent electric lamp, 

 the principle of which has already been given (cf. p. 202). 



Lighting Fixtures. The last few years have pro- 

 duced many changes in the prevailing types of lighting 

 fixtures. Some of the shades and globes are very wasteful 

 of light without possessing much compensating beauty. 

 Indirect lighting is very wasteful of light, and it is also 

 tiring on the eyes. The best light for the eyes will be a 

 well-diffused light with areas of light and shadow as is 

 found in the sunlight. Indirect lighting is well diffused 

 but throws no well-defined shadows, which are so es- 

 sential to normal sight. Probably the light bowl which 

 best meets the requirements of beauty and hygiene is 

 the translucent bowl, which while it reflects some of the 

 light to the ceiling also diffuses much of it directly into 

 the room. This is called semi-indirect lighting. 



For factories direct lighting will be the best and most 

 economical. 



QUESTIONS 



1. What materials were used in windows before glass came 

 into use ? 



2. What is " Jena " glass? 



3. How was the whale-oil lamp made? 



