320 ENVIRONMENTAL CONDITIONS. 



figure 2. There is also clearly indicated a limited region of high 

 summer evaporation in the vicinity of Syracuse, New York. 



(3) The region of intermediate evaporation intensities (from 150 

 to 300 c.c. per week), lying between the other two, of course extends 

 eastward from the California coast to about the one-hundredth meridian 

 of west longitude, where it is nearly replaced by the great embayment 

 of the northern region and by the northeastern termination of the arid 

 region. It then broadens southward to include the Gulf coast and also 

 extends northeastward. It occupies the Atlantic coastal region as 

 far north as southern New England (excepting southeastern Florida). 

 Between the two great southern extensions of the zone of low inten- 

 sities this zone of medium intensities extends northeastward as far as 

 Burlington, Vermont, broadening to include most of Michigan. 



Comparison between plates 55 and 56. — Plate 55, as has been stated, 

 presents a chart of summer evaporation intensities based upon Russell's 

 data, and is here published in order to allow a comparison of our own 

 summer data (1908) with those of Russell (1887-88). As might be 

 expected, the details of these two charts are not at all in agreement, 

 but a study of the two brings out certain features which may be 

 worthy of brief attention. 



(1) It is seen at once that the desert region is clearly shown on both 

 charts. On one scale this zone has an evaporation intensity of over 

 300 c.c. per week; on the other scale, of over 30 inches for the three 

 months, and the geographic areas represented by such intensities are 

 satisfactorily similar in the two cases. 



(2) The region of low intensities of evaporation, characterized by 

 indices below 150 c.c. on the 1908 chart, may be taken to correspond 

 to the region of intensities below 15 inches on the other chart. Such a 

 convention shows, not an agreement between the two, but such differ- 

 ences as might be expected to occur between charts for different 

 summers, even though these were derived by the same methods. On 

 the chart from Russell's data we find the zone of low evaporation 

 (below 15 inches) to extend southward along the Pacific so as to 

 include the whole coastal region, while in the 1908 chart the corre- 

 sponding zone apparently can not be extended nearly so far south- 

 ward. On the 1888 chart, instead of the southward-projecting lobe of 

 the zone of low intensities, west of the Great Lakes (shown on the 

 other), this northern zone merely widens to include all of the Great 

 Lakes and the country west of them to the middle of the Dakotas, and 

 continues eastward to the Atlantic coast. On approaching the coast 

 its southern boundary (plate 55) still bends southward and south- 

 westward and reaches the continental margin only at the mouth of 

 the Rio Grande, thus producing the counterpart of the eastern or 

 Atlantic lobe of this zone (below 150 c.c.) on the 1908 chart. Thence 

 the isoatmic line of 15 inches (plate 55) apparently bends again to the 



