596 Our Surroundings 



heating unit. In places where the night rate for electricity is 

 cheaper, the heating is usually done at night. The current is shut 

 off during the day, and the hot water stored in the tank at night is 

 automatically released to the radiators as needed. 



Electricity would be the ideal heating agent for home fur- 

 naces if it were not so expensive. Wherever electric furnaces 

 have been put into operation they have proved very satisfactory. 

 They are perfectly clean, need no attention, are free from the 

 danger of fire, and require no chimney. Whether or not the elec- 

 tric furnace will be the furnace of the future depends on our 

 ability to generate electricity on a larger scale and at a much 

 cheaper rate than at present. 



The Thermostat. One of the most useful accomplishments 

 of modern mechanics and engineering is automatic control. More 

 and more labor-saving and safety devices for automatically con- 

 trolling machinery are appearing each year. The thermostat, a 

 device for regulating the temperature of buildings automatically, 

 has made a great advance in efficient heating. 



In a home, the thermostat is usually placed on a wall in one 

 of the rooms on the first floor. It consists essentially of a metal 

 rod or coil that is sensitive to temperature changes, expanding as 

 the temperature of the room becomes higher and contracting as it 

 becomes lower. Sometimes two rods of different metals are 

 fastened side by side. As one expands more slowly than the other, 

 the rods are curved to a greater or less extent with each change 

 of temperature. A dial on the instrument is set at the desired 

 temperature. When the temperature increases, the sensitive rod 

 or coil expands, and when it reaches the point at which the ther- 

 mostat is set (usually 68 to 70 F.) an electrical contact is made 

 which sets up an electric current. This current operates controls 

 which either close the drafts (in the coal furnace) or cut down 

 the amount of fuel (in the oil burner and the gas furnace). The 

 electric furnace is also regulated by thermostat. In some types of 

 oil-heated hot-water furnaces which are used also to supply run- 

 ning hot water, the thermostat regulates the heat of the rooms by 

 shutting off the hot water from the radiators. 



When the temperature of the room falls below the point at 



