“Physicist’s Fire” 
with the Texas Fireframe® Grate 
"Amazing amount of heat" BETTER HOMES 
AND GARDENS', "Easy to start" TIME ; "slow- 
burning” NEW YORK TIMES, “No rotation or 
stirring of the logs” SCIENTIFIC AMERICAN . 
"2.6 x more efficient" POPULAR SCIENCE. 
"Easy to maintain" D. J. Ticko, New Fairfield, 
CT. “Does a fantastic job" Frank Stanton NYC. 
For full scientific description, see L Cranberg. 
Am. Jour. Physics, June '81 Reprints on request. 
Grate Model S-25: 25" front width, 2I"back width. 13" 
deep Model KS-25: same, heavs-duty, gift-boxed 
Model U-25: 25x21x15. Model U-17: 17x14x13. 
Model U-33: 33x29x 15. Copyrighted instructions. 
S-25 @$44.95(26#); U-25 @$44.95 (28#) 
U-17 @$36.95(20#); U-33 @$56.95 (35#) 
KS-25 @$51.95(31 #); Reprint (s-a envelope) 
Add 10 Tc for shipping in U S ; Enclose check or 
Visa, MC # Exp. Date 
Name 
Address 
City State Zip 
TEXAS FIREFRAME CO. 
P.O. Box 3435 Austin, Texas 78764 
Marcia Ascher and 
Robert Ascher 
CODE OF THE 
QUIPU 
A Study in Media, 
Mathematics, and 
Culture 
At the height of their civilization the 
Incas had no system of writing, but 
instead used quipus — colored 
cords, knotted in a special manner — 
to record and transmit information 
Based on a study of quipus found in 
Inca graves during 19th- and 
20th-century excavations. Code of the 
Quipu presents a fascinating 
anthropological and mathematical 
study of the problem of interpreting 
artifacts from a distant culture 
paper $8.95 
The University of 
Michigan Press 
Dept FA P.O. Box 1104 
Ann Arbor. MI 48106 
KEEPING WARM 
cost. As the price of down has escalated, 
the newly developed synthetic materials 
have become of greater interest to the 
military. The Army also routinely ex- 
pects to conduct field operations at tem- 
peratures of — 40°F, and in the evalua- 
tion of its extreme cold weather sleeping 
bag, stringent test requirements were 
set: the bag would not be considered 
acceptable unless a soldier could get at 
least six hours of uninterrupted sleep at 
-40°. The sleeping bag that passed this 
test and is now in the Army’s inventory 
contains polyester as well as some strate- 
gically placed down. (It should also be 
noted that synthetic insulation materials 
are nonallergenic, they do not usually 
develop any noticeable odors, and they 
are resistant to attack by microorgan- 
isms. These features, along with the 
materials low moisture pickup, are of 
considerable importance to the Army.) 
For a number of years, efforts have 
been made to supplement the insulation 
of clothing by creating a reflecting layer 
that would reduce the body’s heat loss 
through radiation. Even under ordinary 
indoor conditions, about 50 percent of 
the total heat loss through the skin takes 
place through radiation. Ideally, to keep 
Scanning electron micrographs reveal 
the structure of natural and synthetic 
insulation materials. The insulating 
properties of the materials depend 
on their ability to trap still air. 
us warm, our clothing should incorpo- 
rate a reflective layer that would return 
to the body some of the heat lost 
through radiation. This concept has 
been explored for a number of years but 
without success. Part of the reason is 
that the infrared characteristics re- 
quired in a reflective layer can usually 
be achieved only by means of a continu- 
ous bright metallic surface. If that sur- 
face becomes broken or coated with a 
foreign substance (such as dirt or a body 
excretion), its reflectance characteris- 
tics would be significantly reduced. In 
addition, for a reflective layer to work, a 
finite distance must be maintained be- 
tween the emitting and reflecting sur- 
faces. This would require a spacer mate- 
rial that would keep the two surfaces 
apart and not allow any significant heat 
conduction. To date, no such material 
has been found. 
Perhaps the most adventuresome new 
concept in cold weather clothing derives 
from recent information concerning po- 
lar bears and harp seals. A few years 
ago, an attempt to photograph these 
animals from the air to obtain a popula- 
tion count proved difficult because 
white bears and white harp seals do not 
show up against white ice. The photog- 
raphers then experimented with infra- 
red film on the reasonable assumption 
that creatures containing warm blood 
might emit radiation in the infrared 
range that could be recorded on infrared 
film. To the photographers’ surprise, the 
infrared exposures were equally disap- 
pointing and did not differentiate sig- 
nificantly between the harp seals and 
polar bears and the ice on which they 
96 
