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Show 155 We see from this comparison that July at Fort Mohave counts among the hottest periods of the globe. A table taken from tbe records of the post by the kind permission of the authorities may find here a suitable place. It shows the monthly mean of all the 7 a. m. observations, that of the 12 m. and of 9 p. m. in 1873. March . ...................... r . . . - r ..,,,-- April May July October 7 A. M. F. 47o. 9 47.6 58.6 64 .0 69 .1 81 .7 91.4 85.6 78 8 64.0 54 .1 45.1 18 M. F. 630.8 68.3 81.9 83.0 88 .3 104 .1 110.8 101 .4 108.0 86 .3 77 .0 56.8 9P. M. F. 560.7 53 .6 68 .4 69 .7 78 .8 69 .3 98 .7 68 .8 88 .8 74 .0 67.1 51 .8 As in barren countries the development of heat by insolation on one hand is just as powerful as the loss of heat by radiation in absence of sunlight on the other, December is here observed to be the coolest month, and the sudden transitions from May to June and from September to October. How insignificant, compared with these conditions, appear the changes of temperature between winter and summer on the coast at Santa Barbara) The following table showing this is taken from the Santa Barbara Press: Month. 1878. January February March April * * y June Monthly mean. Fahrenheit 51O. 00 | 54 57 60 63 69 .00 .00 .00 .00 .00 Month. 1878. July A u g u s t . . . . , . . . , September October , November December Monthly Fahrenheit 680. OO 69 .00 67 .00 64 .00 60 .00 63 .00 In Loe Angeles, some 30 miles from the coast, the contrasts are already increased, July reaching a mean temperature of 75° F., January 52° F. The temperature of the soil is generally above that of the air in* sunshine, but this is more the case in barren stretches of the desert than anywhere else; indeed, temperatures of 150° F. of the soil can easily be observed when the air has but 112°. While, however, the surface loses much by radiation during the night, and has at sunrise that of the air, the earth in a foot depth retains still a high degree of heat. I found it one morning still 94° F., when at the same time the surface and the air had but 73° F. In regard to the temperature of the Colorado River, it may be mentioned that from middle of July to middle of September it was never foand below 78° F., and not above 82°. 5. How small this variation compared with that of the air! The temperature of the Rio Grande in Colorado and New Mexico was found in 1874 to be, within small variations, 63° F. from July to October. Humboldt found the average temperatures of Rio Apure and Orinoco during the hottest months to be 27° C, or 80°. 6 F. In regard to the relative humidity of the air, great variations may, a priori, be expected where the daily extremes of temperature are great. Thus, the relative humidity August 6 was, at sunrise, 0.526, ( saturation = 1.0,) while at 3 p. m. = 0.093. Rohlfs* observed as the mean relative humidity in August at Ghaaames ( Sahara) = 0.330, and in July = 0.275. The lowest relative humidity was found in November, 1865, at Murznk, ( Sahara,) at 0.07, ( dry bulb = 82° F., wet bulb = 55° F.) But not only the relative humidity is subject to a great range, but also the absolute. While this was observed in the Colorado Valley after a heavy shower to be increased to 15 grams per cubio meter, it amounted at dry weather only to 6, sometimes 3. Still lower figures, however, were obtained in the fall of 1874 in Northern New Mexico, ( see Annual Report of Explorations and Surveys west of one hundredth Meridian for 1874.) • His extensive meteorological reports are published in Peterman's Goegr., Mitthe-lungen, 1872. |
