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tion of the living body and of the evolution of dress. Then, 
illustrating his remarks by drawings on the blackboard and 
enlivening them with numerous anecdotes, Dr. Williams said :— 
Clothing serves man as a means of protection, and for esthetic 
purposes. 
The following properties should be studied in clothing 
materials, from a health standpoint :— 
(1) Conduction of heat. 
(2) Power of stimulating or irritating skin. 
(3) Power of absorbing moisture, and porosity to air. 
(4) Power of absorbing light and heat rays. 
Heat Conduction.—Some substances, when brought in contact 
with a heated body, rapidly remove its heat and conduct it 
along their substance. They are called good conductors. 
Excepting under conditions of great external heat, good con- 
ductors when touched by our bodies feel cold: they remove 
body heat. Linen is a better conductor than wool; and if on 
a cold winter’s night one turns in between linen sheets the bed 
feels far colder than it would if the sheets were taken away and 
wool blankets brought in contact with the skin. Bad conductors 
of heat are therefore warm clothing materials. 
Gases are bad heat conductors ; yet, if the body were exposed 
unclothed to the atmosphere it would be rapidly chilled. This 
is the result of convection currents. The air in immediate con- 
tact ‘with the body is warmed; it expands and rises, and cold 
currents of air flow down and take its place. This process con- 
tinues, and large amounts of heat removed. If convection 
currents are stopped, air may be made a valuable clothing 
material. Thus the layers of air between bedclothes form a 
warm clothing: the bedclothes prevent convection currents. 
Two thin garments are warmer than a single thick one: there 
is a layer of imprisoned air between them. Loosely-woven 
fabrics are warmer than closely-woven ones: air fills the space 
between the fibres, and friction A/us attraction stops the convec- 
tion currents. 
The power of heat conduction of a clothing material depends 
upon (1) the substance of which it is composed, and (2) the 
way it is woven ; loosely-woven materials being worse conductors 
of heat. 
ORDER OF HEAT-CONDUCTING PoWER OF DIFFERENT FIBRES. 
Cold clothing. 
Cool clothing. 
Warm clothing. 
Very warm clothing. 
Linen = Best conductor 
Cotton = Good conductor 
Silk = Fairly bad conductor 
Wool =: Worst conductor 
Hei tl | 
