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SCIENCE. 



[N. S. Vol. XXIII. No. 593. 



siderable, although by reason of the pre- 

 vailing high temperature it remains far 

 above dew-point and so persists in notably 

 stable condition. The volume of vapor is, 

 of course, due to the proximity of the 

 Pacific and the Gulf whence it is derived; 

 its stability is due to the much higher tem- 

 perature of the land surfaces over which it 

 is carried by the prevailing air-drift, and 

 the consequent warming of the air and 

 rise of the dew-point. Of course the 

 zone is atmospheric rather than terres- 

 trial, meteorologic rather than geographic, 

 and variable in position and character, 

 with many factors of both configuration 

 and climate; in some measure it grades 

 into the fog-belt in both space and time; 

 yet the observations, incomplete as they 

 are, indicate that the vapor zone parallel- 

 ling the Pacific coast is a definite physical 

 entity. 



On considering the relations of the vapor 

 zone to the Californian Gulf, it was at once 

 seen that the general climate and config- 

 uration of the region must tend greatly to 

 increase its extent and enlarge its efficiency 

 as a factor affecting what may be called the 

 continental climate of the interior. Dur- 

 ing the summer the prevailing wind-drift 

 over the region is eastward and northeast- 

 ward, i. e., from the open Pacific over the 

 prominent backbone of the peninsula of 

 Lower California and thence over the gen- 

 erally warmer waters of the enormously 

 long trough forming the Californian Gulf, 

 so that the volume of vapor would nat- 

 urally exceed that drifting inland over an 

 unbroken shore-line; then, once within the 

 great sub-aerial trough, this vapor may not 

 easily escape backward against, or in any 

 other direction than with, the prevailing 

 air-currents ; it may not even flow down 

 the trough to its open mouth 500 to 1,000 

 miles away, by reason of the great distance 

 and the internal friction of vapor and air ; 

 hence it must form a vast reservoir of 



vapor overflowing (occasionally or steadily 

 as conditions may determine) northeast- 

 ward. The effective capacity of this reser- 

 voir must be greatly increased by the pre- 

 vailing character of the land surface, of 

 which from 50 per cent, to far more than 

 90 per cent, is bare white sand or rock 

 from which heat passes rapidly and con- 

 stantly by reflection and radiation and 

 convection into the atmosphere, so that the 

 air is highly heated and the vapor firmly 

 fixed within it; it must be increased also 

 by the augmented diathermancy of the at- 

 mosphere and the resulting intensity of 

 insolation on the land surface attending 

 the relative drying of the atmospheric mass 

 with its rise in temperature; the effective 

 capacity must be still further increased by 

 the barrier forming the western rim of the 

 trough (the sierras making up the backbone 

 of the Californian peninsula) which tends 

 to retard and check the westward-moving 

 atmospheric wave marking the semi-diurnal 

 increase in pressure consequent on morning 

 insolation. These factors culminate in 

 summer when insolation is strongest; and 

 they would seem adequate to account for 

 the persistent daily summer pressures in the 

 gulf-trough which have already attracted 

 the attention of climatologists.^- In short, 

 the preliminary survey of the climatology 

 of southwestern Arizona indicates that just 

 as the Californian Gulf is one of the 

 world's greatest tide producers (its spring 

 tides increasing from little more than two 

 " The barograph was carried from Yuma to 

 Tinajas Altas at the courteous instance of Ob- 

 server Hackett , and with the approval of Chief 

 Moore in the hope of obtaining better liglit on the 

 character and distribution of these summer pres- 

 sures, and it is probable that when the records 

 are discussed they will be found to corroborate 

 the inferences from temperature and moisture ob- 

 servations; although on looking backward over 

 the summer's work it is easy to see that the 

 barograph records would be much more valuable 

 had another instrument been kept at Yuma for 

 comparison. 



