258 PEINCIPLES OF THE MECHANICAL THEORY OF HEAT. 



carefully conducted experiments. With this view he occupied a small hemieti- 

 cally-closcd chamber, constructed of deal-boards, and lighted by a glass window, 

 the contents of which chamber measured about four cubic metres. At one end 

 of this structure was a chair on which he sat when occupied with the develop- 

 ment of heat imder conditions of repose. At the other end was a tread-wheel, 

 the axis of which passed, but so as to be air-tight, through the wall, and was 

 connected on the outside with such an apparatus that by the turning of the 

 wheel a mechanical work was executed. The quantity of this labor performed 

 at each revolution of the wheel is manifestly equal to the lifting of the bodily 

 weight of the experimenter to a height represented by the circumference of the 

 wheel. By means of a counter adapted to the axis of the tread-wheel, the 

 number of revolutions in a given time could be counted, while the quantity of 

 external mechanical work done in an hour could be determined with great 

 accuracy. 



Before the mouth of the experimenter a valve apparatus was attached, from 

 which a caoutchouc tube was carried to a gasometer which furnished the air 

 required for breathing, while a second tube of like material passed to another 

 gasometer which received the exhaled gases ; these, as well as the air inhaled, 

 were carefully analyzed. The chamber was placed in the midst of a larger 

 apartment, the temperature of which varied but little and slowly. Sensitive 

 thermometers gave the tenq)erature of the air both without and within the cham- 

 ber. If, during repose or labor, the interior thermometer had become stationary, 

 its indication was noted, and the valve apparatus placed before the mouth, so 

 that the consumption of oxygen during an unaltered condition of the experimenter 

 might be ascertained. 



It is clear that if the interior thermometer ceased to rise, the loss of heat in 

 the chamber through its walls had become equal to the quantity of heat which 

 the experimenter developed. By a series of preliminary experiments. Him had 

 determined what quantity of heat must be developed within the chamber, in 

 order to maintain within and without definite ditFerences of temperature. With 

 this view a flame of hydrogen gas, supplied by a constant stream, was suffered 

 to burn in the interior of the chamber. For a definite magnitude of the flame, 

 when the condition of equilibrium is attained, a determinate difference of tem- 

 perature within and without the chamber is established ; and when the quantity 

 of hydrogen consumed in a given time is ascertained, we can calculate what 

 quantity of heat has been developed in that time, since we know how many miits 

 of heat are developed by the burning of one gram of hydrogen, {§ 277.) From 

 the repetition of these experiments for different sizes of flame, Hirn obtained 

 the empirical law on which depends the excess of temperature in the interior from 

 the quantity of heat there developed, and he could thus deduce, in later experi- 

 ments, from the observed difference of temperature the quantity of heat developed 

 by the experimenter. 



When, during such an experiment, Hirn occupied the chamber, he found that, 



with absolute rest of his person, 29.65 grams of oxygen were consumed in an 



hour, while the development of heat during that time amounted to 155 units of 



155 

 heat, [calories,) being -, or 5.22 units of heat to one gram of oxygen. 



When, on the other hand, the experimenticr labored on the tread-wheel, so 

 that the work done in an hour amounted to 27448 metre-kilograms, the con- 

 sumption of oxygen in that space of time was 131.74 grams, while the quantity 

 of heat developed, as indicated by the thermometer, amounted to 251 units. 



In the state of rest, however, the 131.74 grams of oxygen consumed would 

 be 131.74 X 5.22=087.68 units of heat, and thus 436.68 would be exhibited 

 more than had in fact been developed; but instead of the vanished 436.68 units 

 of heat, work had been done, partly without, on the tread-wheel, and partly 

 within, in the oro^anism itself. 



