'Action of the Atmosphere upon newly -deepened Soil. 42 



has been found necessary to take means to render it palatable 

 even in agricultural districts." 



Mr. Lawes has found at Rothamsted, 20 miles from London, 

 that when the wind came from that metropolis it contained sooty 

 particles. As soot is known to contain ammonia, it may there- 

 fore be to some extent a source of that ingredient in the at- 

 mosphere. 



But it must not be supposed that we are thoroughly acquainted 

 with all the constituents of the air, for the means at present 

 possessed for determining them are insufficient to detect very 

 minute quantities of matter. This is evident from the fact that the 

 miasms of marshes owe their noxious qualities to some ingredient 

 of a nature too subtle to be detected by the present chemical 

 analysis ; and Seguin, in examining the infectious atmosphere of 

 an hospital whose odour was almost intolerable, could discover 

 no appreciable peculiarity in its composition. A variable 

 amount of watery vapour is always diffused through the atmos- 

 phere: its absolute quantity is usually greatest in summer on ac- 

 count of the temperature being higher ; but the dryness of the 

 air depends less upon the absolute quantity of vapour that may 

 be present than on its condition as to saturation. The warmer 

 the air is, the more water will it contain ; hence the atmosphere is 

 moister during summer than in winter, although the absolute 

 quantity of sensible vapour in it may be much less ; but few data 

 exist as to the amount of this ingredient in the air. According 

 to Dr. Anderson, of Glasgow, 1000 volumes of air contain on an 

 average about 8 volumes of watery vapour. Amongst the con- 

 stituents of the atmosphere may also be enumerated the substance 

 termed ozone, which has of late years been brought under notice 

 by Dr. Schonbein, of Basle, and which would appear to be very 

 frequently present. Traces of iodine have also been found by 

 Chatin to exist in the atmosphere. 



The properties of these different ingredients of the atmosphere, 

 and their actions, chiefly in so far as they are related to the 

 subject of tliis paper, may now be touched upon. 



Oxygen^ Ozone. — These two substances are taken together, as 

 their action is probably similar, differing mainly in degree. The 

 chief chemical j)r<)p(Mties of the air are perhaps due to the presence 

 of this element (which is a transparent colourless gas somewhat 

 heavier than common air), tlie greater part of the changes which 

 the njineral and organic matter of the soil undergo proceeding 

 from its numerous and powerful affinities. For most simple 

 bodies it has a very strong attraction, combining with all tlie 

 elementary bodies save perhaps fluorine. The act of combining 

 witli it is called oxidation ; this may take place very vapidly 

 wit!i t!ie evolution of heat and light, giving rise to the plieno- 



