324 THE HUMAN MOTOR 



The air has free access to the central chamber, the latter has 

 a large side door, shown in dotted lines, to allow the subject to 

 enter the apparatus, which is afterwards hermetically sealed 

 during the experiment. 



The subject is seated in the interior on a stool. His head 

 projects through a circular hole, round the edges of which is fixed 

 a rubber cap which goes over the head. Respiration, therefore, 

 takes place in the open air, although the atmosphere inside the 

 calorimeter is separated from the external atmosphere. 



The outlet chamber contains a fan S, capable of exhausting 

 600 cubic metres of air per hour. 



The inlet chamber N has three air intakes open to the external 

 atmosphere, and an anomometer can be fixed to each of these 

 openings (200). 



Knowing the sections, s lf s 2 , s 3 , of the air intakes and the 

 average speeds, v v v. 2 , v 5 , of the air current, the volume of 

 air can be calculated by the sum of the products : 



S 1 V 1 +5.^2 -fSgflg ... =SV. 



Accurate thermometers reading to ^ of a degree are placed 

 in front of and behind the subject to give the amount by which 

 the air is heated. Let V be the average speed of the air during 

 the experiment and SV is the volume in litres. The weight of a 

 litre of air being 1-293 gr., the total mass M will be : 



M = S X V x 1-293 grammes. 



Correcting for the atmospheric pressure H and the temperature 

 t of the air, the expression becomes : 



The increase in temperature 6 will therefore correspond to : 



Q = M x X 0-237 cal. 

 0-237 cal. being the specific heat of air. 



It is possible, with this simple and accurate apparatus, to 

 measure the thermal waste at different speeds and temperatures 

 of the air current ( 175). 



251. Thermal Conductivity. We can estimate this waste with 

 various garments by taking into account their co-efficient of 

 conductivity or of transmission c ( 170) . The following are some 

 values of that co-efficient, in addition to those already given : 



