The humidity caused by an abundant rainfall in any low, hot country is usually enough to unfit it for human habitation. The combined effect of heat and moisture upon a fertile soil causes an excess of both growing and decaying vegetation that fills the atmosphere with noxious vapors and disease producing germs. The sultry air is so oppressive that it is more than physical endurance can bear. The particles of vapor which float in the atmosphere absorb and hold the heat until it becomes like a steaming hot blanket that is death to unacclimated life. All of this is changed where siccity prevails. The rapid evaporation quickly dispels the vapors and the dry heat desiccates the disease creating germs and makes them innocuous.
The effect of heat upon the body is measured by the difference in the actual and sensible temperatures, as recorded by the dry and wet bulb thermometers. When both stand nearly together as they are apt to do in a humid atmosphere, the heat becomes insufferable. In the dry climate of Arizona such a condition cannot occur. The difference in the two instruments is always great, often as much as forty degrees. For this reason, a temperature of 118 degrees F. at Yuma is less oppressive than 98 degrees F. is in New York. A low relative humidity gives comfort and freedom from sunstroke even when the thermometer registers the shade temperature in three figures.
A dry, warm climate is a stimulant to the cutaneous function. The skin is an important excreting organ that is furnished with a large number of sweat glands which are for the dual purpose of furnishing moisture for cooling the body by evaporation and the elimination of worn out and waste material from the organism. As an organ it is not easily injured by over work, but readily lends its function in an emergency in any effort to relieve other tired or diseased organs of the body. By vicarious action the skin is capable of performing much extra labor without injury to itself and can be harnessed temporarily for the relief of some vital part which has become crippled until its function can be restored.
A diseased kidney depends particularly upon the skin for succor more than any other organ. When the kidneys from any cause fail to act the skin comes to their rescue and throws off impurities which nature intended should go by the renal route. For this reason diabetes and albuminuria, the most stubborn of all kidney diseases, are usually benefited by a dry, warm climate. The benefit derived is due to an increase of the insensible transpiration rather than to profuse perspiration. The air of Arizona is so dry and evaporation so rapid that an increase in perspiration is scarcely noticeable except when it is confined by impervious clothing. The disagreeable feeling of wet clothes which accompanies profuse perspiration in a damp climate is changed to an agreeable sensation of coolness in a dry one.
The atmosphere of Arizona is not only dry but also very electrical, so much so, indeed, that at times it becomes almost painful. Whenever the experiment is tried, sparks can be produced by friction or the handling of metal, hair or wool. It affects animals as well as man, and literally causes "the hair to stand on end." The writer has on various occasions seen a string of horses standing close together at a watering-trough, drinking, so full of electricity that their manes and tails were spread out and floated in the air, and the long hairs drawn by magnetic attraction from one animal to the other all down the line in a spontaneous effort to complete a circuit. There are times when the free electricity in the air is so abundant that every object becomes charged with the fluid, and it cannot escape fast enough or find "a way out" by any adequate conductor. The effects of such an excess of electricity is decidedly unpleasant on the nerves, and causes annoying irritability and nervousness.
The hot sun sometimes blisters the skin and burns the complexion to a rich, nut-brown color, but the air always feels soft and balmy, and usually blows only in gentle zephyrs. The air has a pungent fragrance which is peculiar to the desert, that is the mingled product of a variety of resinous plants. The weather is uniformly pleasant, and the elements are rarely violently disturbed.
In the older settled sections of our country, whenever there is any sudden or extreme change in the weather of either heat or cold, wet or dry, it is always followed by an increase of sickness and death. The aged and invalid, who are sensitive and weak, suffer mostly, as they feel every change in the weather. There is, perhaps, no place on earth that can boast of a perfect climate, but the country that can show the fewest and mildest extremes approaches nearest to the ideal. The southwest is exceptionally favored in its climatic conditions, and is beneficial to the majority of chronic invalids.
Atmospheric pressure is greatest near the earth's surface, and exerts a controlling influence over the vital functions. Atmospheric pressure is to the body what the governor is to the steam engine, or the pendulum to the clock. It regulates vital action, insures safety and lessens the wear and tear of machinery. Under its soothing influence the number of respirations per minute are diminished, the heart beats decreased in frequency, and the tired brain and nerves rested. It is often better than medicine, and will sometimes give relief when all other means fail.
Arizona has a diversity of altitudes, and therefore furnishes a variety of climates. The elevations range from about sea level at Yuma to nearly thirteen thousand feet upon the San Francisco mountains. By making suitable changes in altitude to fit the season it is possible to enjoy perpetual spring.
Because Arizona is far south geographically it is only natural to suppose that it is all very hot, which is a mistake. In the low valleys of southern Arizona the summers are hot, but it is a dry heat which is not oppressive, and the winters are delightfully pleasant. In northern Arizona the winters are cold and the summers cool. There is no finer summer climate in the world than is found on the high plateaus and pine-topped mountains of northern Arizona. Prescott, Williams and Flagstaff have a charming summer climate, while at Yuma, Phoenix and Tucson the winter weather is simply perfect.