448 RELATION OF HEAT-PRODUCTION TO WORK. 



a certain amount of work say, raise a weight by a suitable arrangement. This 

 work must, of course, be accomplished by the potential energy of the heating 

 material. At the end of this experiment, the temperature of the water will be 

 much less than in the first experiment, i. e., fewer heat-units have been transferred 

 to the calorimeter when the engine was heated than when it did no work. 



Comparative experiments of this nature have shown, that in the second experi- 

 ment the useful work is very nearly proportional to the decrease of the heat 

 (Him). 



In good steam-engines only ^V> an ^ m the very best ^, of the potential energy 

 is changed into mechanical energy, while #- passes into heat. 



Compare this with what happens within the body : A man in a 

 passive condition forms from the potential energy of the food between 

 2J-2f million calories. The work done by a workman is reckoned at 

 200,000 kilogramme-metres. 



If the organism were entirely similar to a machine, a smaller amount 

 of heat, corresponding to the work done, would be formed in the body. 

 As a matter of fact, the organism produces less heat from the same 

 amount of potential energy when mechanical work is done. There 

 is one point of difference between a workman and a working machine. 

 The workman consumes much more potential energy in the same time 

 than a passive person ; much more is burned in his body, and hence, 

 the increased consumption is not only covered, but even over-com- 

 pensated. Hence, the workman is warmer than the passive person, owing 

 to the increased muscular activity ( 210, 1, 6). Take the following 

 example : Hirn (1858) remained passive, and absorbed 30 grm. per 

 hour in a calorimeter, and produced 155 calories. When in the calori- 

 meter he did work equal to 27,450 kilogramme-metres, which was 

 transferred beyond it; he absorbed 132 grm. O, and produced only 

 251 calories. 



In estimating the work done, we must include only the heat equivalent of the 

 work transferred beyond the body; lifting weights, pushing anything, throwing 

 a weight, and lifting the body, are examples. In ordinary walking, there is no loss 

 of heat (apart from overcoming the resistance of the air); when descending from a 

 height there may be increased warmth of the body. 



The organism is superior to a machine in as far as it can, from the 

 same amount of potential energy, produce more work in proportion to 

 heat. Whilst the very best steam-engine gives J of the potential 

 energy in the form of work, and as heat, the body produces -f- as 

 work and -J as heat. Chemical energy can never do work alone, in a 

 living or dead motor, without heat being formed at the same time. 



218. Accommodation for Varying Degrees of 

 Temperature. 



All substances which possess high conductivity for heat, when 

 brought into contact with the skin, appear to be very much colder or 



