66 
TRANSACTIONS OF THE TEXAS ACADEMY OF SCIENCE. 
tion of heat or cold as felt by the higher orders of animal life the sensible 
temperature. Neither of these is a measure of the other. The fact is 
well known to meteorologists, that the thermometer alone can not indi- 
cate the sensible temperature, but that the humidity of the air must be 
considered in connection with the actual temperature. This fact is also 
known to dwellers in the arid region, but it is not known to the majority 
of otherwise intelligent people throughout the world. 
“Where the percentage of atmospheric moisture is high, both extremes 
of temperature are felt to be greater than the thermometer indicates. 
Everybody knows something about that condition of the weather which 
is variously termed ‘sultry/ ‘close/ or ‘muggy. 5 These terms describe 
the result of a combination of heat and moist air. This is the condition 
which exists commonly in the tropical regions of the world where the 
rainfall is heavy, and in the same way, though in a smaller degree, 
throughout the United States outside of the arid region. It is especially 
noticeable in the States bordering on large bodies of water, such as the 
Gulf of Mexico or the Great Lakes, and is conspicuously absent from 
the greater portion of Arizona. 
“In the dry air of this territory sunstrokes are unknown, while in the 
Mississippi Valley and in the States lying eastward whole columns of the 
newspapers are filled with accounts of prostrations from heat; and the 
fatalities are numerous whenever the thermometer indicates 90 degrees 
Fahrenheit, or upwards. At many places along the seacoast, where the 
humidity always remains near the point of saturation, a temperature of 
85 degrees brings excessive discomfort, and exertion or exposure to the 
sun is extremely hazardous. Men and the lower animals perform in 
safety their customary labor beneath the cloudless skies of Arizona, under 
the highest temperature ever experienced here. The dry air induces ex- 
ceedingly rapid evaporation of the abundant perspiration, thus keeping 
the body at a comparatively low temperature. As a matter of course, 
the supply of fluid must be maintained, hence the great thirst so often 
experienced by travelers in desert regions, and the imperative necessity 
for an adequate supply of drinking water. Of all the lives lost on the 
desert stretches of Western America — and their number is not small — 
not one is directly attributable to heat, but to thirst. The experienced 
traveler provides an ample supply of water and fearlessly invades the 
worst desert yet discovered. 
“An amount ranging from fifteen to perhaps thirty degrees, accord- 
ing to the humidity, should be subtracted from the maximum actual 
temperatures in Arizona, during the hot season, to indicate the sensible 
temperatures. In like manner, the dry air of the arid regions enables 
extremely low temperatures to be endured without discomfort. The 
winter cold of the Canadian Northwest Territory is much less disagree- 
