OBSERVATIONS OF CHANGE OF TEMPERATURE 



43 



Thermal Equivalents. 



Numbers expressing the Relative Quantities of Various Kinds 

 of Matter which are Equivalent in Thermal Change. Water 

 is taken as Unity. So-called ' Specific Heats ' are the Reci- 

 procals of these Numbers. 



We may, perhaps, now begin to regard thermal changes as 

 conditional, not on the volumes nor the masses of the bodies 

 taking part in them, but rather on something which is within 

 the body itself. Equal masses are not equivalent, nor are 

 equal volumes. Further investigation will show that under 

 certain conditions the minute particles which are supposed to 

 constitute matter are thermally equivalent. 



34. To Measure the Numerical Value of the Temperature- 

 change occurring in Surrounding Bodies when 1 gram of 

 Ice Liquefies. A weighed quantity of water in a glass beaker 

 is prepared, and its temperature ascertained by a thermometer. 

 Ice which has been standing in the room for some time, so as 

 not to have a lower temperature than C., and which has 

 been dried, is added in quantity afterwards determined by 

 re-weighing the beaker and water. When all the ice is melted, 

 and the whole has been thoroughly stirred with the thermo- 

 meter, the temperature is again noted. 



A known quantity of ice has changed to water without 

 change of temperature (remaining at C.), and has then 



