Mat 11, 1906.] 



SCIENCE. 



729 



feet at its mouth to twenty-five feet at its 

 head), so its aerial portion forms an effect- 

 ive mechanism for promoting the flow and 

 retarding the ebb of the atmospheric tide; 

 and it may be noted that just as the oceanic 

 tides produce astoundingly turbulent cur- 

 rents in the gulf waters mid-length of its 

 troiigh, so the air-vapor tide results in the 

 astonishingly sudden wind storms and 

 strong williwaws of Tiburon Island and 

 the adjacent coasts. 



The extent of this vapor reservoir must be 

 large, though variable from season to sea- 

 son (greatest in summer, least in winter), 

 and from day to day according to a variety 

 of factors and conditions which— like those 

 of climatology in general — are commonly 

 cumulative in effect. The coastward 

 boundary of the vapor zone must shift with 

 the conditions governing the presence or ab- 

 sence of fog, etc. ; while the inland bound- 

 ary must be determined from place to 

 place by altitude, local configuration, pres- 

 ence or absence of floral covering, and other 

 factors influencing temperature, dew-point, 

 precipitation and storm centers. Tinajas 

 Altas and Yuma would seem to lie in the 

 vapor belt or reservoir, while Mohawk, 

 Parker and other stations in the western 

 division of Arizona would seem to lie with- 

 out it. Proceeding from these points, with 

 the guidance of the July and August storms 

 in the ranges east of Sierra Gila, the sum- 

 mer inland margin of the vapor belt or 

 reservoir may be drawn southeastward 

 from Rio Colorado at a point twenty-five 

 miles above Yuma to Rio Gila ten miles 

 east of Gila City, and thence to and along 

 Sierra de la Cabeza Prieta, crossing the 

 international boundary near the eastern 

 line of Yuma County; and thence more 

 nearly southward and roughly parallel with 

 the gulf coast to Hermosillo (Sonora) and 

 on— gradually approaching the gulf— to 

 regions beyond the influence of this great 

 geographic trough : though it may be noted 



that the general vapor belt (apparently so 

 greatly expanded about the Californian 

 Gulf) must parallel much of the Pacific 

 coast wherever configuration favors, per- 

 haps attaining next best development in 

 western Peru, where broad Piedmont plains 

 of distinctively desert climate intervene 

 between the Andes and the coast. Within 

 the expansion of the Californian trough 

 the vapor belt would seem especially po- 

 tent in its influence on continental climate, 

 through the development of storm centers 

 if not otherwise — indeed, a considerable 

 proportion of the effective storm centers 

 traced in their course across the country 

 during recent years, through the observa- 

 tions of the Weather Bureau, originate in 

 this region. 



Incidentally, the observations at Tinajas 

 Altas throw light on a question suggested 

 by earlier notes on the climate of Arizona 

 and Sonora, i. e., the question as to rela- 

 tion between what may be called the Cali- 

 fornia type of climate, characterized by a 

 winter rainy season and a summer dry sea- 

 son, and the Sonora type, comprising a 

 winter rainy season and a summer rainy 

 season, with intervening dry seasons; for 

 in the light of the Tinajas Altas records it 

 would appear that the types correspond, 

 except that in the Sonoran region the effect 

 of the vapor reservoir above the gulf in 

 summer (when the land surfaces are hot- 

 test) is to develop storms drifting into the 

 interior from the zone in which the vapor 

 is for a time imprisoned. 



A CONSTRUCTIVE SUGGESTION. 



If the foregoing inferences are valid, it 

 is manifest that the conditions existing 

 about the Californian Gulf exercise impor- 

 tant influence on the climate of the conti- 

 nent, and are worthy of correspondingly 

 careful consideration. Any investigation 

 might properly begin with observations 

 made at a few suitably located stations. 



