182 



FUELS AND THEIR USES 



How temperature is measured. What do we mean by 

 temperature? We are aware that our bodies are warm, 

 and that ice is cold. Measured in de- 

 grees of temperature, the body is 98.6 

 degrees, while melting ice is 32 degrees 

 Fahrenheit. The common house ther- 

 mometer is an instrument consisting of 

 a fine bore, sealed glass tube with a bulb 

 at the lower end. Mercury or colored 

 alcohol fills this bulb and extends part 

 way up the tube. As heat makes mer- 

 cury expand, it rises in the tube when 

 it gets warmer, and degrees of temper- 

 ature are marked on the thermometer 

 (see diagram). There are two kinds of 

 measurements, the one used by scien- 

 tists, known as the Centigrade scale, 

 while the Fahrenheit scale is used in this 

 country for ordinary purposes. Ther- 

 mometers have come into very general 

 use, and we should all know how to read 

 them and understand what they mean. They are useful 

 as regulating devices in cooking, as we often find them in 

 the oven doors. We also use them for regulating the 

 temperature of our rooms. The room temperature should 

 never be allowed to go over 70 degrees Fahrenheit in winter 



House thermometer. 



Clinical thermometer. 



and the air should not be allowed to get dry, as such con- 

 ditions increase our liability to colds when we leave the 

 house to go out of doors. One type of thermometer has 



