Irrigation has been practiced in different portions of the Arid Region for the last twenty-five or thirty years, and the area cultivated by this means has been steadily increasing during that time. In California and New Mexico irrigation has been practiced to a limited extent for a much longer time at the several Catholic missions under the old Spanish regime. In the history of the settlement of the several districts an important fact has been uniformly observed--in the first years of settlement the streams have steadily increased in volume. This fact has been observed alike in California, Utah, Colorado, and wherever irrigation has been practiced. As the chief development of this industry has been within the last fifteen years, it has been a fact especially observed during that time. An increase in the water supply, so universal of late years, has led to many conjectures and hypotheses as to its origin. It has generally been supposed to result from increased rainfall, and this increased rainfall now from this, now from that, condition of affairs. Many have attributed the change to the laying of railroad tracks and construction of telegraph lines; others to the cultivation of the soil, and not a few to the interposition of Divine Providence in behalf of the Latter Day Saints. If each physical cause was indeed a _vera causa_, their inability to produce the results is quite manifest. A single railroad line has been built across the Arid Region from east to west, and a short north and south line has been constructed in Colorado, another in Utah, and several in California. But an exceedingly small portion of the country where increase of water supply has been noticed has been reached by the railroads, and but a small fraction of one per cent. of the lands of the Arid Region have been redeemed by irrigation. This fully demonstrates their inadequacy. In what manner rainfall could be affected through the cultivation of the land, building of railroads, telegraph lines, etc., has not been shown. Of course such hypotheses obtain credence because of a lack of information relating to the laws which govern aqueous precipitation. The motions of the earth on its axis and about the sun; the unequal heating of the atmosphere, which decreases steadily from equator to poles; the great ocean currents and air currents; the distribution of land and water over the earth; the mountain systems--these are all grand conditions affecting the distribution of rainfall. Many minor conditions also prevail in topographic reliefs, and surfaces favorable to the absorption or reflection of the sun’s heat, etc., etc., affecting in a slight degree the general results. But the operations of man on the surface of the earth are so trivial that the conditions which they produce are of minute effect, and in presence of the grand effects of nature escape discernment. Thus the alleged causes for the increase of rainfall fail.