E. J. Russell and E. H. Richards . 321 



atmosphere. It- is known^ that this oxiciation proceeds under the action 

 of the silent electric discharge, and it ma}' well form part of the normal 

 atmospheric phenomena. 



In reviewing the evidence for and against these various possibilities 

 one is driven to conclude that the ammonia in country rain probably 

 arises from several sources and not from one only. The sea, the soil, and 

 towns and cities may each contribute their share. Of these the soil 

 appears to be the most important in view of the fact that the amount 

 brought down by the rain is at a maximum in the summer months when 

 biochemical activity in the soil is at its highest, and at a minimum in 

 winter when biochemical activity in the soil is low. This does not amount 

 to proof of the origin of the ammonia because the higher ammoniacal 

 content of summer rain is affected by another factor: the rain during 

 the summer months is probably on the whole formed at higher levels 

 than that falling during winter months, and, having a greater distance 

 to travel, it would wash out the ammonia from a larger quantity of air 

 than is possible in the case of winter rain. A further effect is discussed 

 on p. 328. 



A certain amount of atmospheric ammonia may also come from the 

 towns: the reality of this source is indicated by the fact that town rain- 

 water is considerably richer in ammonia than country rainwater. This 

 is unlikely to be the chief source, as the ammonia in town rain is high in 

 winter, whereas we have seen it is then at its lowest in country rain. 



The nitric nitrogen also probably arises from several sources. In 

 the early years of the work the amount of nitric nitrogen recorded 

 was only one-third that of the ammoniacal nitrogen, but for the greater 

 part of the period of the observations it was one-half. Of late years there 

 have been some exceptionally high values, causing the nitric nitrogen 

 to become equal to the ammoniacal nitrogen. These changes indicate 

 an artificial rather than a natural origin for part of the nitrate. But 

 it cannot all arise in this way, for it is widely distributed over the world. 

 Some of it may arise by direct combination of nitrogen and oxygen 

 during lightning and other major electrical disturbances. For the greater 

 part the close correlation between the amounts of nitric nitrogen and 

 of ammoniacal nitrogen indicates either a common origin, or a formation 

 of nitric compounds from ammonia by the minor electrical disturbances 

 and electrical stresses normally occurring in the atmosphere, or in some 

 other way. 



1 See W. G. Mixter, Amer. Journ. Set., 1898 [iv], 6, 217-224. 



