124 ELEMENTARY SCIENCE 



mometer is a measure of temperature rather than of heat. 

 The amount of heat in a substance is another thing. That 

 may be measured by another instrument, the calorimeter, 

 of which more later. 



The thermometer was invented by Galileo, in 1593, 

 one hundred and one years after the discovery of America. 

 Before that there was no science of heat; men judged of 

 it solely by their feelings. When men began to study heat 

 with the aid of the thermometer they discovered a number 

 of things about it which they could not discover by their 

 feeling alone. Thus the thermometer shows that the 

 temperature of boiling water does not increase however 

 long it continues to boil, a thing that was not discovered 

 when the temperature of objects was judged by fingers 

 instead of thermometers. Thermometers also show that, 

 when heat is applied, the temperature of some substances 

 rises much more rapidly than the temperature of others. 

 Thus mercury is thirty times easier to heat than water; 

 it requires only one-thirtieth as much heat to raise the 

 temperature of a given quantity of mercury one degree 

 as it requires to raise the same amount of water one 

 degree. 



Such facts gave the early scientists much more light on 

 the subject of heat than they had had before. Their 

 theories as to heat had to be revised in the light of new 

 evidence. This sort of thing is constantly happening in 

 science. Investigators are constantly discovering new 

 facts which require the recasting of old theories. Now as 

 to heat, men have had a number of interesting theories. 

 It was once supposed to be due to the presence of a mysteri- 

 ous fluid known as caloric. And as to fire, the ancient 

 Greeks believed that it was due to the presence of another 



