354 ENVIRONMENTAL CONDITIONS. 



plates 57 to 62. This rektive-humidity chart also agrees, in general, 

 with the moisture-ratio charts just mentioned, by showing an east- 

 ward projection of the semihumid area from Nebraska to New England. 

 The eastern humid area occupies the Gulf coast from the Rio Grande 

 eastward, practically all of the Atlantic coast (excepting northern 

 New Jersey and southeastern New York), northern New England, 

 northern New York, and northern Michigan. In its northeastern 

 portion this chart resembles that of plate 61 more than any of the other 

 moisture-ratio charts. 



(3) Pebcentages Representing Nobmal Mean Relative Air Humidity for the Yeab. 



(Table 19, Plate 66.) 



Our data for this index are taken directly from Stockman's table. 

 They are reproduced in the second column of table 19, and are repre- 

 sented by the chart of plate 66. 



This chart also shows a pronounced general agreement with our 

 charts for the Transeau moisture ratios. The general zonation of the 

 country is again shown by broad hues, but the lines for the value 65 

 on plate 65 are here represented by those for the value 70. The semi- 

 arid region is here thus characterized by values between 50 and 70, 

 and the values for the semihumid region lie between 70 and 75. The 

 line for the value 72 has been added in the central part of the country, 

 to emphasize the eastern lobe of the semihumid area (shown also on 

 plates 57 to 61 and on plate 65). An area of values a little below 70 

 is shown about St. Louis, Louisville, and IndianapoHs, thus differing 

 from plate 65, but agreeing, in general, with plates 57 to 61. The 

 eastern humid region is here shown as much like that of plate 65, but 

 the hue for 75 here lies considerably farther south in the regions of the 

 Great Lakes and of New England. In this respect plate 66 resembles 

 plates 57 to 60 more than plates 61 and 65. 



(4) I^ebcentages Representing Mean Relative Air Humidity for June, July, and August 



1908. (Table 19, Plate 67.) 



The data for these indices were obtained from the Monthly Weather 

 Review for 1908, the means for the three separate months being simply 

 averaged in each case. The results are given in the fourth column of 

 table 19 and are charted in the usual way in plate 67. 



This chart has the hues for the index values 50, 70, and 75 repre- 

 sented as full lines, to exhibit the general zonation of the country, just 

 as in the case of plate 66. The northwestern humid area (values above 

 75) here extends southward, along the Pacific coast, nearly to Los 

 Angeles, California, and the corresponding semihumid area reaches to 

 the Mexican boundary. The arid area is depicted in much the same 

 way as on the other two charts of relative humidity, but is not quite 

 as extensive here as in the other cases, this being due, no doubt, to the 

 effect of the characteristic summer rains in western Texas and New 



