222 



portion is only one of degree. The temperature will change witli alti. 

 tude and latitude, and tlie moisture among the mountains will be greater 

 tlian on the i)lains. 



That we may enter more intelligently upon the consideration of the 

 climate of Colorado, we will biietly glance at the various influences that 

 control a climate. 



Great altitude has perhaps the most important influence on climate, 

 because of tbe rarity of air that accompanies it, producing rapid evap- 

 oration, dryness, variability, and extremes of temperature, clearness 

 of skies, and all the efl'ects opposite to those of the sea-level, where the 

 thick stratum of humid atmosphere intercepts the sun's rays, retains 

 heat, obstructs radiation, and produces equability of temperature. Low 

 humidity is the main characteristic of high elevations, and is caused 

 principally by the lower temperature reigning at such elevations, but 

 also by the diminution of atmospheric pressure, allowing less moisture 

 to be held in a given space of air at a given temperature than at lower 

 levels. Authorities state that there is an average lowering of temi)era- 

 ture of three degrees Fahrenheit for each thousand feet of ascent, and 

 this cooling lessens the capacity of air to contain moisture. 



Latitude has a strong influence on climate, acting in much the same 

 way as altitude ; the effects of a high degree of latitude being, in a gen- 

 eral waj^, similar to those of a great altitude. Professor Loomis states 

 that beyond the parallel of sixty degrees north latitude, at a short dis- 

 tance from the ocean, the mean annual rain-fall seldom exceeds 10 

 inches. 



Distance from the ocean naturally i)romotcs dryness, and to this fact 

 is due, in no small degree, the uniform lack of humidity in the atmos- 

 phere upon the extensive plateaus of^Wyoming, Colorado, and New 

 Mexico, which is not found in the high altitudes of Switzerland. The 

 evaporation constantly going on over the ocean and all bodies of water, 

 supplying the atmosphere with moisture, which returns to the thirsty 

 land in rain, is wanting in the elevated interior of our continent. And 

 there can be no satisfactory compensation on our open plains for this ab- 

 sence of water distribution, as long as there are no forests, undergrowth, 

 or thick grasses to prevent evaporation and drying of the laud, and to 

 provide by their natural reservoirs and springs and differences of tem- 

 perature a substitute for the ocean. Afar inland position also has a pow- 

 erful influence upon temperature. The specitic heat of laud being only 

 one quarter that of water, it both absorbs and gives out heat more rap- 

 idly', consequently the more land the greater the heat and the wider the 

 fluctuation, especially when there is nothing to obstruct the sun's rays 

 or the earth's radiation. 



High mountain ranges exert a powerful influence upon the moisture 

 conditions of a climate, by intercepting the air currents which come 

 from a distant, warm, damp region. Such currents are quickly brought 



