THE BALANCE OF NUTRITION 



221 



or kilogram calorie (Cal.), equal to one thousand small calories, 

 is employed, while for still larger quantities the Therm, equal 

 to one thousand large calories, may be used. In the following 

 pages the term calorie signifies the large, or kilogram, calorie, 

 unless the contrary is expressly stated. 



Certain units of gravitation energy are also frequently used, 

 especially in mechanics, the more important ones being the 

 gram meter, the kilogram meter and the foot pound. The 

 gram meter is the energy required to raise a weight of one gram 

 vertically through one meter in opposition to gravity, the kilo- 

 gram meter is the energy required to raise a weight of one kilo- 

 gram through one meter, and the foot pound is the energy re- 

 quired to raise a weight of one pound through one foot. Since 

 the force of gravity varies at different points on the earth's 

 surface these units as thus defined are not invariable. Taking the 

 average force of gravity at sea level, however, as equal to 980.5 

 dynes, the relations between these various units are as follows : 



EQUIVALENCE OF UNITS OF ENERGY 



309. Measurement of heat energy. Quantities of heat 

 are measured chiefly in two ways, viz., by their effects in raising 

 the temperature of some substance or in changing its state of 

 aggregation. Instruments for measuring quantities of heat 

 are called calorimeters, i.e., heat measurers. 



In the first method, as already implied in the definition of the 

 calorie (308), water is ordinarily used as the calorimetric sub- 

 stance. 1 For example, if the quantity of heat to be measured 

 can be transferred without loss to a kilogram of water, and if 

 the temperature of the water is thereby raised 2 C., it is evi- 

 dent that the quantity of heat imparted to it is two large calo- 



1 Other substances than water may, of course, be employed, but water is usually 

 the most convenient. 



