THE TWO THERMOMETER SCALES 



61 



ment is then heated, so that bulb and tube are completely filled, and 

 the open end is sealed by melting the glass. 



The thermometer is then graduated, that is, the " degree" marks are 

 put on it. First the bulb is put into melting ice 

 (Fig. 53), and the point at which the mercury comes 

 to rest is marked the freezing point. Then water 

 is made to boil under " standard pressure" (cf. 40), 

 and the bulb is put into the steam that comes off 



(Fig. 54). The place at which 



the mercury stops is called the 



''boiling point" mark of the 



thermometer. 



FIG. 53. 



Getting the Freezing 

 Point of a Ther- 

 mometer. 



FIG. 54. 



Getting the Boiling 

 Point of a Ther- 

 mometer. 



63. The Two Thermom- 

 eter Scales. The differ- 

 ence between the two common thermom- 

 eters the Fahrenheit and Centigrade 

 thermometers is in the number of de- 

 grees that are put between the freezing 

 point mark and the boiling 

 The maker of the Centigrade 

 He divided the space 



point mark, 

 instrument was Celsius. 



between the two marks into 100 degrees (Fig. 

 55). "Centigrade" means just that: "100 

 degrees" or "steps." Celsius made the freez- 

 ing point of his thermometer 0, and the 

 boiling point 100. If the thermometer tube 

 is of the same bore throughout, and a new 

 mark is made as far above 100 as is below 

 it, the new mark will be 200. In this way 

 the other marks of the thermometer are fixed. 

 The Fahrenheit thermometer is named from 

 its maker, who took for his'O the temperature sca\ entigrade 



