1919] 1CBTK0B0L0GY. 809 



the aid of two maps, showing (l) the average annual number of rainy days In 

 the United States, and (2) the mean annual probability ol rainy days In tin- 

 United States. 



Briefly summarizing, the author states thai "the ninety-fifth meridian 

 divides the country into two halves, over the .astern of which the average 

 number of rainy days exceeds 100 a year, while over the western, with certain 

 exceptions, rain falls on less than LOO dass. I'lcin the ninety lifth meridian 

 eastward there is an increase in the number Of rainy days inward the Atlantic 

 Ocean and especially toward the Great Lakes (maximum Of 170). From the 

 ninety-fifth meridian westward there is a general decrease except on the north 

 Pacific coast, where there is a maximum of 180 rainy days. . . . 



"Tlie extreme northwestern coast and the Great Lakes have the greatest 

 probability of rain. Both of them are regions of marked cyclonic activity. 

 one day in every two days is likely to be rainy on the coast of Washing* 

 East of the Great Plains the probability of rain is more than 20 per cent. Over 

 much of this area, especially toward the coast and the Great Lakes, it is over 

 30 per cent, and more than 35 per cent of all the days of the year are likely 

 to be rainy over a considerable portion of the Great Lakes region and on the 

 New England coast. The central Appalachians have a slightly higher rain prob- 

 ability than the surrounding lowlands, while to leeward, chiefly in Virginia, 

 there is a small area under 30 per cent. 



" With decreased cyclonic control and less favorable rainfall conditions, 

 most of the vast area west of the one hundredth meridian and east of the 

 Pacific slope mountains has less than 20 per cent, the rain probability being 

 somewhat greater over the Rocky Mountains and decreasing to less than 5 per 

 cent in the arid Southwest. It is seen that the New England coast and much 

 of the Great Lakes area have more than seven times as many rainy days as 

 southwestern Arizona; that the eastern margin of the Great Plains has half, 

 or less than half, as many as the Oregon coast; that the southern California 

 coast has the same rain probability as extreme southeastern Texas. 



"The seasons of greatest and of least probability of rain may easily be 

 inferred from a knowledge of the seasonal distribution of rainfall in various 

 sections of the country. The marked cyclonic activity of the colder months 

 readily suggests that winter will bring the greatest probability of rain on the 

 Pacific coast, over much of the western plateau area, and in considerable B 

 tions in the East, heading up toward the Great Lakes. Late spring and early 

 summer bring the greatest probability over most of the Great Plains and east- 

 ward to the Mississippi Valley. The southern Atlantic and the Gulf coast, as 

 well as the southwestern interior, have their greatest probability in middle or 

 late summer and early autumn. About one-half of the United States has the 

 greatest probability of rain in the warmer months. Summer, which is the 'dry 

 season,' brings the minimum rain probability on the Pacific coast and over most 

 of the plateau region. East of the Rocky Mountains autumn is the dominant 

 season of minimum probability." 



Ammonia and nitrous nitrogen in the rain water of southwestern Alaska, 

 J. W. Shipley (Ohio Jour. Sri., 19 (1919), No. 4, pp. 230-23 ',).— Examination- 

 rainfall collected at different times from August 19 to September 1". T.>17. 

 showed the almost entire absence of ammonia in the rainfall of southwestern 

 Alaska. Nitrous nitrogen was found in every case except one. 



The nitrogen compounds in rain and snow, 1'. T. Sinrr and R. L. DOBBAHCI 

 (Proc. and Trans. Roy. Soc. Canada, 3. «er., // i 1917), Sect. HI. /*/>. 63-12; ahs. 

 in Sci. Abs., Sect. A.- Phya., 82 (1919), No. 254, pp. 59, 60; Jour. Ohem. 8oa 

 [London], 116 (1919), So. 67G, /. p. 116).— Continuing previous observations 



