10 



cury, and mark this position also by means of an ink 



spot. 



These two points are called the boiling point and the 

 freezing point of water, and the distance 

 between them is divided into equal parts 

 called degrees. On the Fahrenheit scale it 

 is divided into 180 degrees, and on the Cen- 

 tigrade into 100 degrees. The lower point 

 on the Fahrenheit scale is marked 32, and on 

 the Centigrade o ; while the higher point 

 on the Fahrenheit scale is marked 212, and 

 on the Centigrade 100. 



A bulb of this sort filled with mercury 

 and graduated so that unknown tempera- 

 tures may be determined is called a ther- 

 mometer. The Fahrenheit thermometer is 

 used in the United States ; the Centigrade 



is used throughout most of Europe and for all scientific 



purposes. 



EXPERIMENT 2. TEMPERATURE CURVES 



Draw two straight lines OX and OYon a piece of coor- 

 dinate paper, and represent temperatures by distances 

 above OX, and time intervals by distances to the right 

 of OY. Let one space above OX represent one degree 

 of temperature, and one space to the right of OY one 

 five-minute interval. Any point on AB will represent a 

 temperature of 12, since it is twelve spaces above OX, 

 and any point CD will represent a time interval of forty 

 minutes, since it is eight spaces to the right of OY. 

 The point at the intersection of these two lines, there- 

 fore, represents a temperature of 12, forty minutes after 



FIG. 3. Deter- 

 mining the lower 

 point on a ther- 

 mometer. 



