SCIENCE OF COMMON THINGS. 



191 



Different varieties of thermometers. 



Construction of pyrometers. 



dred and eighty. According to Reaumur, water freezes 

 at 0, and boils at 80 ; according to Centigrade, it 

 freezes at 0, and boils at 100 ; and according to Fah- 

 renheit, it freezes at 32, and boils at 212; the last, very 

 singularly, commences counting not at the freezing 

 point, but 32 below it. 



The differences between these instruments can be easily seen by refer- 

 ence to Fig. 41. 



1261 In what countries are the Reaumur and Centigrade thermometers 

 generally used ? 



fieaumur is in general use in Germany, and the 

 Centigrade in France / but for scientific purposes the 

 Centigrade is almost universally adopted. 



12362 At what temperature does mercury freeze ? 



At about 39 below the zero of Fahrenheit's thermo- 

 meter. 



1263 How are degrees of cold more intense than this measured f 



By using a thermometer filled with alcohol colored 

 red, as this fluid when pure does not congeal at 100 

 Fahrenheit below zero. 



1264 At what temperature does mercury boil f 



At 660 Fahrenheit. 



1265 How are temperatures greater than this determined f 



By means of the expansion of solids and instru- 

 ments founded upon this principle are commonly called 

 pyrometers. 



Fig. 42. 

 Ihe construction of the pyrometer is represented in Fig. 42. A repre- 



