The Nation: That Wind-Chill Factor

At U.S. bases in the Arctic and Antarctic, the newcomer must quickly learn the 30-30-30 Rule of Survival: when exposed to a 30-m.p.h. wind at —30° F., human flesh freezes solid in 30 seconds.

The killing factor is wind chill. The term, glibly cited by TV weathermen but only dimly understood by a flash-frozen populace, is based on a scale that precisely correlates temperature and wind force. Wind chill—expressed in meteorological phraseology as "equivalent temperature"—measures the difference, in impact on exposed skin, between what the thermometer registers and the wind delivers.

The meteorologists' wind-chill table starts at still air (0-m.p.h. wind) and ranges...