The Sonoran province is notably warm and dry. The vapor-laden air-currents from the Pacific drift across it and are first warmed by conduction and radiation from the sun-scorched land, to be chilled again as they roll up the steeper roof-slope to the crest; and the precipitation flows part way down the slopes, both eastward and westward from the Sierra Madre—literally the Mother (of waters) range. A climatal characteristic of the province is two relatively humid seasons, coinciding with the two principal inflections of the annual temperature-curve, i. e., in January-February and July-August, respectively. In the absence of meteorologic records the temperature and precipitation maybe inferred from the observations at Yuma and Tucson,[5] which are among the warmest and driest stations in America, or indeed in the world; though it is probable that such points as Caborca, Bacuachito, and Hermosillo are decidedly warmer and perhaps slightly moister than Yuma. The ordinary midday summer temperature at these points may be estimated at about 110° in the shade (frequently rising 5° or 10° higher, but dropping 20° to 50° in case of cloudiness); the night temperature at the same season is usually 50° to 75°, though during two-thirds of the year it is liable to fall to or below the freezing point. The sun temperature is high in comparison with that measured in the shade, the exposed thermometer frequently rising to 150° or 160°, according to its construction, while black-finished metal becomes too hot to be handled, and dark sand and rocks literally scorch unprotected feet. The leading characteristic of the temperature is the wide diurnal range and the relatively narrow annual range; another characteristic is the uniformity, or periodic steadiness, of the maxima, coupled with variability and nonperiodicity of the minima. [5] The following monthly and annual meteorologic summaries, compiled from United States Weather Bureau records at these stations, have been kindly furnished by Prof. Willis L. Moore, Superintendent of the Bureau. The tabulated records represent the observations of twenty years at Yuma and ten years at Tucson. Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Year Absolute maximum temper- ature, Fahr.: Yuma 81 91 100 105 112 117 118 115 113 108 92 83 118 Tucson 84 85 95 101 106 111 110 109 106 97 89 82 111 Absolute minimum temper- ature, Fahr.: Yuma 22 25 31 40 44 52 61 60 50 41 31 25 22 Tucson 14 20 24 32 38 39 64 60 46 31 23 11 11 Mean maximum temper- ature, Fahr.: Yuma 65.1 70.7 78.5 85.4 93.2 101.2 106.7 104.9 99.6 87.2 75.0 67.4 86.6 Tucson 62.9 67.0 74.5 81.4 91.4 100.2 99.0 94.8 92.2 82.8 71.5 63.7 81.8 Mean minimum temper- ature, Fahr.: Yuma 42.0 46.1 50.8 55.1 61.4 68.3 77.2 77.6 70.5 58.5 48.8 44.7 58.4 Tucson 34.9 41.5 44.0 48.1 55.3 63.8 75.0 73.6 67.3 52.1 42.5 35.1 52.8