496 PHYSIOLOGY AT THE FAKM. 



the head of vital work, heat work, mechanical work, or mental 

 work. The heat, however, so produced, in the case of vital 

 work, mechanical work, and mental work, is severally meta- 

 morphosed so as not to become sensible that heat only be- 

 coming sensible which falls under the head of heat work. 



There is a general agreement among authorities as to the 

 relation between the production of carbonic acid in the living 

 body, and the joint amount of hea.t work and of the other kinds 

 of work therein developed ; but in regard to several ulterior 

 points, as will be seen hereafter, controversies exist of a very 

 perplexing description. 



Effect of falling from a height on the temperature of a 

 body. The relation, however, between the generation of tem- 

 perature and the production of mechanical force is the point 

 towards which our attention in the first instance is to be 

 specially directed. 



When a body falls from a height to the ground, the tempera- 

 ture of that body is increased it does not matter whether the 

 body be solid or liquid. Thus it has been discovered that 

 when any quantity of water is let fall from a height of 772 

 feet, the temperature of that water rises one degree of Fahren- 

 heit's thermometer. But it is readily ascertained that the 

 mechanical effect which the impact of such a body falling 

 through that height is capable of producing is equal to what 

 is required to raise 772 times the same mass through the 

 height of one foot. Whence the fact that one Ib. of water falling 

 through 772 feet obtains a rise of temperature equal to one 

 degree of Fahrenheit, and the correlative fact that that rise of 

 temperature in one Ib. of water is sufficient to raise 772 Ib. 

 weight of matter through a height of one foot, constitute the 

 standard of measurement relative thereto in what is called the 

 "conservation of energy." 



The production of carbonic acid the measure of the total 



