5
stated that the entire region west of the 98th degree of west longitude, with the exception of a small portion of western Texas, and the narrow border along the Pacific, is a country of comparatively little value to the agriculturist; and, perhaps, it will astonish the reader if we direct his attention to the fact that this line, which passes southward from Lake Winnepeg to the Gulf of Mexico, will divide the whole surface of the United States into two nearly equal parts. This statement, when fully appreciated, will serve to dissipate some of the dreams which have been considered as realities, as to the destiny of the Western part of the North American continent. Truth, however, transcends even the laudable feelings of pride of country; and in order properly to direct the policy of this great confederacy, it is necessary to be well acquainted with the theatre on which its future history is to be enacted, and by whose character it will mainly be shaped."
The marked features of the vast region of which we speak is the very great difference of the heat of the days and nights.
Colonel Emory, who made the first survey across the continent, says:—"On the 23d of October we retired with the thermometer at 70 degrees, and awoke in the morning shivering, with the mercury marking 25 degrees, notwithstanding our blankets were as dry as if we had slept in a house. … These low morning temperatures were found to characterize the whole country between Upper Mexico, and the settlements near Great Salt Lake, the summer observations for three' successive days being at 14 degrees and 15 degrees. At Salt Lake, Utah Territory, it is difficult to grow Indian corn, because of the extreme aridity of the air, though the mean temperature is 10 degrees above that necessary in a moist climate. The local cooling at night, and the higher heats by day, are both unfavorable in this arid atmosphere."
To show these facts from more,recent authority, we quote from the report of the Agricultural Bureau for the year 1865 (pages 528 and 529):—"The desert and mountainous regions of our own continent furnish ample illustration of these phenomena of radiation." Captain Beckwith, in his narrative of the Central Pacific Railroad Survey, remarks:—"We observed the greatest contrasts between the heat of the day and of the night in these mountain valleys, from noon to three p. m. the thermometer standing at 87 degrees to 90 degrees, and at night falling below the freezing point."
That accomplished English scholar, Professor John Tyndall, says that it may be safely predicted, that whenever the air is dry the daily thermometric range, or the difference between the extremes of heat and cold, will be very great. In his celebrated lecture on "Radiation," before the University of Cambridge in 1865, in discussing aqueous vapor in relation to terrestrial temperatures, he remarks:—"This aqueous vapor is of the utmost conse-consequence to the life of the world. Imagine the superficial molecules of the earth trembling with the motion of heat, and imparting it to the surrounding ether; this motion would be carried rapidly away and lost to our planet, if the waves of ether had nothing but the air to contend with in their natural course. But the aqueous vapour takes up the motion of the ethereal waves, and becomes thereby heated, thus wrapping the earth like a warm garment, and protecting its surface from the deadly chill which it would otherwise sustain."
The observations of meteorologists furnish important though hitherto unconscious evidence of the influence of this agent. Wherever the air is dry, we are liable to daily extremes of temperature. By day, in such places, the sun's heat reaches the earth unimpeded, and renders the maximum high; by night, on the other hand, the earth's heat escapes unhindered into space, and renders the maximum low. Hence the difference between the maximum and minimum is greatest where the air is driest. In the plains of India, on the heights of the Himalaya, in Central Asia, and in Australia, wherever drought reigns, we have the heat of day forcibly contrasted with the chill of night. In the Sahara itself, where the sun's rays cease to impinge on the
