THE " KATA " THERMOMETER 



447 



atmosphere raises this value three times. These values 6 and 18 are maximal 

 values for the cooling power of the atmosphere in rooms where sedentary- 

 work is being carried out. For heavy physical work, the cooling power must 

 be increased in proportion to the severity of the work. 



It may be surrounded by wet muslin and the experiment repeated. The 

 dry bulb instrument gives an indication of the possibilities of heat-loss 

 by radiation and conduction, while the wet bulb indicates, in addition, the 

 possibility of heat-loss by evaporation of moisture. 



The Comfimeter is a form of kata-thermometer designed to give an imme- 

 diate indication of the cooling property of the air in rooms. It consists of a 

 cylindrical metal box in which is inserted an electric incandescent lamp. 



On the top of the box is fixed an inverted metal funnel having a long 

 stem. An ordinary thermometer is hung from inside the upper part of 

 this stem so that about two-thirds of its length remains outside the instru- 

 ment. When the lamp is lit, air enters the comfimeter by means of holes in the 

 cylindrical box and the heated air rises and leaves by the orifice in which 

 the thermometer is hung. The whole apparatus is cooled by radiation, 

 convection and by conduction. When the comfimeter gives a reading of 

 30° C, this indicates a cooling power of about 7 millicalories per square 

 centimetre of effective cooling surface per second — an ideal condition. If, 

 now, the box be screened from draughts, the comfimeter thermometer will 

 rise to 45° or maybe 50° C. On permitting free ventilation, the instru- 

 ment will again record a temperature of about 30° C. A lower temperature 

 than this is a sign of too rapid cooling. The designer. Professor L. Hill, says 

 that as long as schools, factories, etc., are kept with the comfimeter indicating 

 somewhere about 30° C, conditions suitable for work will be maintained. 



Work of itself, as is well known, causes production of heat in 

 the body. Some 75 per cent, of the energy generated in muscular 

 contraction is dissipated as heat. In spite of the large quantity 

 of heat thus liberated, the body temperature does not increase to 

 any great extent. It may rise by about 1° C, depending on the 

 cooling value of the environment as well as on the severity of the 

 work. The following figures from Pembrey (Table LXX.) illus- 

 trate the influence of the rate of cooling on the body temperature 

 after severe work : 



TABLE LXX 



Soldiers on Completing a March of Seven Milks 



On the colder day with a percentage difference of about 15 

 between dry and wet bulb temperatures, i.e. under good cooling 

 conditions, the temperature and heart-rate of the soldiers showed 



