LIGHT 57 



varies. If a pound of water and a pound of olive oil were 

 placed side by side in similar dishes on a stove, it would be 

 found that the olive oil increases in temperature about 

 twice as fast as the water, i.e. it takes about twice as 

 much heat to raise water as it does to raise the same weight 

 of olive oil one degree. In fact, it takes more heat to 

 raise a given weight of water one degree than it does to 

 raise the same weight of almost any other known substance. 



In Experiment 27, the resulting temperature from the 

 water mixture was much higher than from the shot mix- 

 ture. The shot has much less capacity for heat. The 

 quantity of heat required to raise the temperature of a 

 certain mass of a substance one degree compared to the 

 quantity of heat required to raise the same mass of water 

 one degree is called the specific heat of that substance. 

 The specific heat of olive oil is .47, of shot .03. That is 

 it takes .47 as much heat to raise a given mass of olive oil 

 and .03 as much heat to raise a given mass of shot one 

 degree as it does to raise corresponding masses of water 

 one degree. In order to compare different quantities of heat, 

 physicists have taken as the unit of measure the quantity 

 of heat required to raise the temperature 

 of one gram of water through one degree C. 

 This unit is called a calorie. 



29. Light. The sun is not only the 

 source of almost all the heat of the earth 

 but also of its light. We have developed 

 artificial self-luminous bodies such as 

 candles, lamps, electric lights, but none 

 of these compares with the light given 

 by the sun. The stars also furnish a Fig * 31 ' 

 little light. Most of the bodies that we know are 

 dark and non-luminous. Sometimes some of these 

 which have polished surfaces reflect the light from a 



