MEASURING OF HEAT 



123 



The lowest temperature obtainable is called absolute zero. 

 This would be a point 459.6 below zero Fahrenheit, or 273.1 

 below zero Centigrade. At this tem- 

 perature no more heat would be pres- 

 ent in a body. 



This simple form of thermometer gives 

 indications of existing temperatures. In sick- 

 rooms, greenhouses and many other places, 

 it is interesting and sometimes necessary to 

 have a knowledge of what the temperature 

 has been. For this purpose a thermometer 

 capable of giving maximum and minimum 

 temperatures is used. * > 



The creosote in the tube in the center 

 expands when the temperature increases, 

 driving the quicksilver down on the left-hand 

 side and up on the right-hand side, thus in- 

 creasing the air pressure in the right-hand 

 bulb. As the right-hand side shows an increase 

 in its scale reading it is called the "Heat" 

 or "Maximum" side of the tube. 



If the temperature lessens, the creosote 

 will contract so that the quicksilver will fall 

 on the "Heat" side and rise on the "Cold" 

 or " Minimum " side, which shows the ther- 

 mometer scale decreasing. 



Indices are carefully made and inserted in 

 the tubes above the levels of the quicksilver 

 which can be used to indicate the highest and 

 lowest points the thermometer has reached 

 since its last setting. 



The index is a miniature glass bottle with 

 a small piece of steel wire inside it. Steel 

 is used so that the index can be raised or 

 lowered by means of a magnet which can 

 be moved up and down in front of the 

 tube, 



FIG. 97. Maximum and Min- 

 imum Thermometer. 



