212 



POPULAR SCIENCE MONTHLY. 



supplied in several experiments in which 

 the man did no considerable external 

 work was 2,500 large calories. The ex- 

 cess in the work experiment was there- 

 fore 1,226 calories. Dividing the work 

 done, 25G calories, by the excess of en- 

 ergy absorbed, 1,226, and the quotient 

 is .21. Thus 21 per cent, of this excess 

 of energy absorbed was converted into 

 work, or the efficiency of the man as a 

 machine for doing work is 21 per cent. 

 This is far greater than the efficiency of 

 small portable steam engines, such as 

 could be compared with respect to size 

 or power with a human machine, and 

 equals or surpasses that of the largest 



It may be of interest to show how a 

 man's weight varies during twenty-four 

 hours. The accompanying diagrams* 

 give the variation in the weight of the 

 man under investigation in one of the 

 rest experiments; that is, in a four-days' 

 experiment, where no mechanical work 

 was done, except that involved in eating, 

 dressing and making some records and 

 observations within the calorimeter. 

 The routine followed each day was near- 

 ly but not exactly the same, and the 

 fluctuations of weight are accordingly 

 similar but not identical each day. 



Increase of weight is due to food and 

 drink taken into the body and oxygen 



compound condensing engines taken in 

 connection with the most perfect water- 

 tube boilers. 



The bicycle-dynamo combination is 

 not the most effective device upon which 

 to develop mechanical power; and in 

 the experiments quoted no attempt was 

 made to secure the maximum efficiency 

 of conversion of the potential energy of 

 foodstuffs into mechanical energy. Al- 

 though many experiments have already 

 been carried out, further experiments 

 are needed to show more fully what the 

 human machine is capable of doing, and 

 what circumstances are favorable to a 

 high efficiency of conversion. 



respired from the atmosphere. Decrease 

 of weight is due to feces and urine leav- 

 ing the body, and carbon dioxid and 

 water vapor carried away from the lungs 

 and skin. Part of these changes in 

 weight occur more or less suddenly, 

 while the change due to respiration, in 

 which oxygen is absorbed and carbon 

 dioxid and water vapor are evolved, is 

 gradual. In the diagrams the sudden 

 changes are indicated by vertical lines, 

 the numbers indicating the quantity of 

 the change in grams. The gradual 



♦Copied from an article by the writer in the 

 'Physical Review' for March, 1900, 'On the 

 Metabolism of Matter in the Living Body.' 



