82 



JUNIOR GRADE SCIENCE 



liked, but for the sake of comparing one man's observations and ex- 

 periments with those of other people, it is most convenient to graduate 

 all thermometers in the same way. The thermometers used in this 

 country are graduated in two ways (1) the Centigrade scale, (2) the 

 Fahrenheit scale. A third scale the Reaumur scale is extensively 

 used in Germany. 



The Centigrade scale. Here the freezing point 

 is called zero or no degrees Centigrade, written C. 

 The boiling point is called one hundred degrees Centi- 

 grade, and is written 100 C. The space between 

 these two limits is divided into 100 parts, and each 

 division called a degree Centigrade. 



The Fahrenheit scale. On thermometers marked 

 in this way the freezing point is called thirty-two 

 degrees Fahrenheit, written 32 F., and the boiling 

 point two hundred and twelve degrees Fahrenheit, 

 written 212 F. The space between the two limits is 



foiling Point ofWztcr 



" Melting point oflc& 



Centigrade Fahrenheit Reaumur 



FIG. 66. Thermometric scales. 



Fi'.. '".A clinical 

 thermometer. 



divided into 180 parts, and each division is called a degree Fahrenheit. 

 The reason of this difference is interesting. The physicist Fahrenheit, 

 after whom the thermometer is named, obtained a very low tempera- 

 ture by mixing common salt with the pounded ice when marking the 

 lower fixed point, and he wrongly imagined that he had obtained the 

 lowest temperature which could be reached, and called it zero. 



The Re'aumur scale. Upon thermometers graduated according 

 to this scale the freezing point is marked and the boiling point 80, 

 The relation between the three scales is shown in Fig. 66. 



