May 11, 1906.] 



SCIENCE. 



723 



dismantled and the equipment transferred 

 during the night to Wellton en route to 

 Yuma. 



The observations comprised pressure (de- 

 termined by barograph and aneroid), tem- 

 perature, humidity, wind, precipitation and 

 cloudiness. 



The barograph was used in accordance 

 with a courteous suggestion by Sumner 

 Hackett, U. S. weather observer at Yuma, 

 in the hope that its record might throw 

 light in the persistent lows of the Cali- 

 fornia Gulf region. This record has not 

 yet been compared and discussed. 



The wind observations were rendered 

 practically worthless by local conditions; 

 the atmosphere in the gorge was habitually 

 disturbed by dust whirls drifting in from 

 the plain with intensity rapidly increasing 

 as they caught the rock-warmed air-volume 

 between the canyon walls, so that even the 

 pressure was rendered unsteady (in one 

 case a single whirl of momentary duration 

 caused the barograph pen to record a 

 change in pressure of over twenty feet) ; 

 while the arrangement of neighboring peaks 

 and precipices so disturbed the general air 

 currents that their direction could seldom 

 be determined confidently without a 

 journey of two or three miles eastward on 

 the plain, or a three-hours' climb up the 

 granite precipices and peaks. 



From the beginning of experimental ob- 



servation on May 21, the temperature rec- 

 ords (both of the maximum and minimum 

 and of the wet and dry bulb thermometers) 

 seemed notable by reason of a relatively 

 low diurnal range — a range considerably 

 less than that previously noted by the sta- 

 tion agent in connection Avith geologic and 

 ethnologic work in Nevada, Sonora and 

 southern-central Arizona. The minitude 

 of the range, indeed, awakened a suspicion 

 of inaccurate reading and led to the above- 

 noted delay of two days in beginning the 

 more formal record transmitted to the ob- 

 server at Yuma; it also led to a series of 

 experiments with coverings for the wet 

 bulb of the psychrometer, resulting in the 

 adoption of a somewhat thicker and more 

 spongy covering and a longer period of 

 swinging than more humid climates require. 

 Before the middle of June, however, the 

 record developed such consistency as to es- 

 tablish the general accuracy of the observa^ 

 tions. The accompanying Table I., trans- 

 scribed from the original field-sheets, illus- 

 trates the lovmess of diurnal and general 

 ranges in temperature and also in moisture 

 — including rain as well as cloudiness (ex- 

 pressed in tenths of total sky estimated for 

 the visible and inferred for the invisible 

 portions) — during the one hundred days 

 from May 21 to August 28. As shown by 

 this table, the extreme thermometric range 

 during this period was but 62.8°, the range 



TABLE I. TEMPERATURE AND MOISTURE EXTREMES. 



