1916] on The Science of Clothing 563 



The instrument is used (1) dry = cooling by radiation and convec- 

 tion ; (2) wet (surrounded with a giove of damp muslin) = cooling 

 by evaporation, radiation and convection. The difference between 

 the two readings gives the evaporative cooling power. The dry 

 instrument can also be clothed in a woollen glove, and readings 

 taken representing the cooling power of the clothed portions of 

 the body. 



The ordinary dry-bulb thermometer is a static instrument, repre- 

 senting average temperature of surroundings and giving no account 

 of the cooling effect of wind. The Kata-thermometer, on the other 

 hand, is a dynamic instrument like the human body, and represents 

 the rate of heat loss and the enormously important influence of wind. 

 It can be used as a most delicate annemometer.* The wet Kata- 

 thermometer shows the great effect of wind in promoting evaporation 

 of sweat from the skin.f It is an admirable measurer of evaporative 

 power, and should be of great use in determining this in the drying 

 chambers used in so many commercial processes. The Kata-thermo- 

 meter readings show that the cooling power of the atmosphere in 

 confined rooms is like or even worse than that of tropical regions 

 out of doors. The difference in cooling power is enormous between 

 still air and full exposure to wind, such as an outdoor worker 

 endures. Movement of air is of vastly greater importance to our 

 comfort and health than temperature measured by the ordinary 

 thermometer. To test if with natural ventilation there is sufficient 

 movement of the air in rooms the volume of carbon dioxide in the 

 air may be measured, but it should not exceed that in the outside air 

 hy even 1 part in 10,000. There should be no permissible increase. 



Kata-thermometer readings taken with various clothing materials 

 show that the essential heat-retaining power depends on the retention 

 of a layer of still warm air in contact with the body. To keep cool 

 in hot days the one thing necessary is to allow the wind to blow 

 through flimsy, loose, open garments. To keep warm in arctic 

 conditions wind-proof clothing is designed, such as that used in 

 Labrador. Whether the clothing is woollen or cotton in this respect 

 is immaterial ; its thickness and permeability to wind are the 

 essential properties. A woollen stuff when wet does not cling close 

 to the skin, as cotton does, owing to the elasticity of the hair fibres 

 in the woollen garment. The curving hairs keep it off from the 

 skin and so allow a layer of warm air to protect the skin from the 

 cooling effect of wet. Thus a wet woollen is warmer than a wet 

 cotton garment. In no other respect do the hygroscopic properties 

 of clothing materials seem to matter. A shipwrecked man immersed 

 in the sea should not strip, but keep on his woollen clothes, so that 

 the entangled air may keep him warm. A great deal of nonsense is 



* It measures the effect of eddies together with the direct current. 

 t See Trans. Rov. Sec. B., 1916, p. 183. 



2 p 2 



