KATA-THERMOMETER 347 



where A the constant of the instrument, 



F = tlie tension corresponding to 0, the reading on the wet 

 bulb thermometer, 



H = atmospheric pressure, 



t = reading on dry bulb thermometer, 

 and m = maximal vapour tension at t C. 



If .4=0-00082, = 20C., = 16 C., # = 758 mm. Hg., 



F (from a table of vapour tensions) = 13-63 mm. Hg. 



Then /= 13-63 -0-00082x758x4 = 11-16 mm. Hg. 



The maximal vapour tension at 20 C. (from a table) = 17-52 mm. Hg. 



Therefore, the degree of humidity = -^=0-637. 



tn 1 i 'oZ 



The "Kata " thermometer is a large bulbed spirit thermometer. It may 

 be warmed to say 38 C. The time is then taken while it cools to 35 C. 

 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 

 immediate indication of the cooling property of the air in rooms. It 

 consists of a cylindrical metal box in which is inserted an electric incan- 

 descent 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 2/3 of its length remains outside the instrument. 

 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, Prof. L. Hill, says 

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

 cating somewhere about 30 C., conditions suitable for work will be main- 

 tained. 



Work of itself, as is weir 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 2 C., depending on the 

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

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



