1116 
case of clothing such as fur, the true surface is difficult 
to determine. 
We then have, for the surface concerned, 
Q ar exSE x = Paha =F h;) (Oz a Se), (13) 
and 
Q = FihcOs =e Ox); (14) 
hence 
Q Q + exSPy = §. = 6. (15) 
ehe Paha a vhs) 
The following conclusions can be reached from equation 
(15): 
1. Above certain wind speeds (large haz), solar radi- 
ation S becomes ineffective. 
2. For he K (ha + h,), that is, for good insulation, 
the effects of wind (assuming h, to be invariant with 
respect to v) and of solar radiation vanish. 
3. Protection against solar radiation by reflection 
(small ex) is particularly effective in the case of thin 
fabrics (large h,.), deep penetration of the radiation 
being undesirable, of course. Solar rays are best re- 
flected by white surfaces; those originating from sources 
below 1500C (fire), by shiny metals [20]. 
4. The insulation value 1/h, necessary to maintain 
the @ and #, of the body constant can be determined 
experimentally or by calculations on the basis of the 
frigorigraph values 3’. Let Q, ex, and e be the same for 
the body and for the frigorigraph. For the body, 
F, = 4Fy. Finally, let 3. = 2,. It then follows from 
equations (11) and (15) that 
i _ AG = 8) 
2 =i 
in 0 deg C m hr Cal™. (16) 
For clothing comprising several layers (¢ = 1, 2. . .n), 
1 
he +I@Q, |p 
a 1 
x d/h ay x ka/ da ae |p 
where d; and k; denote thickness and thermal con- 
ductivity of the clothing layers, respectively; d, and 
ka are the corresponding values for the intermediate 
layers of air. (Since convection would occur in thick 
air layers, equation (17) is valid only for da < 0.01 m.) 
The factor d, is particularly sensitive to pressure and 
body motion. The function f(v) represents symbolically 
the total effect of wind pressure on insulation (wind 
penetration through porous fabrics and openings; flap- 
ping, etc.). 
The conductivity of cloth (k;) is determined by three 
elements: (1) conduction by the interstitial air, (2) 
conduction along the component of the fabric fiber 
oriented in the direction of heat flow (the same com- 
ponent is responsible for resistance against compression) 
which becomes undesirably high for dense, compressed, 
and wet fabrics, and (8) radiation from fiber to fiber, 
a process which has hitherto not been considered, but 
which becomes noticeable in the case of large fiber 
Separations. With increasing temperatures, the two con- 
BIOLOGICAL AND CHEMICAL METEOROLOGY 
duction terms rise only slightly, but the radiation term 
increases considerably [21]. Table I lists several values 
to illustrate the foregoing considerations. 
Taste I. Hear Conpucriviry anD Drnsity oF 
DIrFERENT MaTEeRIALs 
(According to Buettner (14, 18]) 
k 
i -1throl p 
Material ae (ke m7) 
De ct ee Ran hy Oke eae eee oles chal other a Nee Os 0.023 iL 3} 
Waiter: Fee. SRI eee ay ph eM RYe eet 0.52 1000 
\WwWooll Glow, GWAY. 252 s0cgccov0s0oaca0eane 0.030 100 
Woolkclothtiwetaeeeeeper nner eee 0.092 250 
Wool cloth, dry, under pressure........ 0.085 170 
ASBESTOS. 4. . Pot ta. arnets pat heee tere eee eae 0.079 860 
Glasspiabricy20 Caner reee cae ere 0.027 210 
Clings tiglomm@, GHC), cosconencosassoc0er 0.081 210 
Human skin, upper layer, excised...... 0.18 — 
Human skin (0-2 mm deep), in situ*... 0.32 — 
Human skin (2mm deep), in sitw, cool*. 0.47 _— 
Human skin (2mm deep), in situ, warm*. 3.60 —_— 
* After [14]. They include the effect of blood advection. 
Rain or perspiration increases k;; water in the cloth 
may even freeze, thus causing even higher k;. These 
processes might make the cloth windproof; consider- 
ation must be given to the question when and where 
this water or ice can be eliminated. 
The question of how the extremities should be pro- 
tected in extreme cold is difficult to answer. If the body 
as a whole produces enough heat, even poorly pro- 
tected extremities are safe [40]. On the other hand, 
for geometrical reasons, clothing for the hands and 
feet would have to be prohibitively thick. 
In the case of hot desert winds, loose clothing affords 
protection against overheating and dehydration result- 
ing from the inadequate water supply to the skin 
[1, 19]. 
Breathing. In breathing, a heat exchange A takes 
place which depends on the transferred volume M 
(m* hr‘), the heat capacity and density of the air, 
and the difference in the equivalent temperatures of 
the inhaled and exhaled air. 
The mechanism by which the exhaled air is heated 
and humidified may be conceived of as follows [70]: 
Incoming air having the equivalent temperature J; 
cools the mucous membranes of the upper respiratory 
organs (nose, mouth, throat) by convection. During 
this process the air itself is raised to blood temperature 
and saturated with moisture. The air, returning after a 
brief pause in the lungs, is cooled by the still relatively 
cool, mucous membranes. As long as the mucous mem- 
branes are moist, the air remains saturated and emerges 
from the mouth or nose with the equivalent temper- 
ature, 
J, = 0. + 1.5H,. 
The process may be treated schematically by assuming 
a constant mean membrane temperature. We intro- 
duce as fictitious quantities the equivalent temperature 
of saturation at blood temperature J, and at the average 
temperature of the mucous membrane J,, as well as 
the thermal conductance of the membrane h,, the sur- 
