430 REPORTS ON THE STATE OF SCIENCE. — 1919. 



In Pamphlet No. 34, published by the Ministry of Eeconstruction, on page 13 

 it is stated that the smoke from a single factory chimney, about 20 miles to 

 the weet of London, could be traced and recognised as far as 30 miles to the 

 east of London, i.e., 50 miles from its source. The smoke from this chimney 

 formed one of the most conspicuous landmarks in the South of England for 

 flying machines. This shows the importance of even a single source of impurity. 



Again, there is the fuel-economy side of the question. As will be seen later 

 from the composition of the deposit, a large proportion of the impurity of the 

 air is derived from incomplete combustion of fuel and represents waste. 



I do not propose to delay further over this aspect of the question, as its 

 importance from different points of view has already been brought out, and is, 

 I think, fairly well recognised. It may be well, however, before proceeding 

 further to get some definition of what we mean by atmospheric pollution. 



Normal air may be regarded as consisting of a mixture of various gases in 

 the following proportions : — 



10000 



There also exists a varying proportion of watery vapour, and the term pollu- 

 tion may be regarded as applying to anything that disturbs the above-d^ecribed 

 constitution of the air. But in the present connection pollution is interpreted 

 as relating only to such matter, solid, liquid or gaseous, as is not included 

 in the above list of components. 



There are certain elements of pollution deposited from the air which may be 

 regarded as entirely foreign to the atmosphere. These are tarry matter, car- 

 bonaceous matter derived from smoke, and sulphates. Other impurities, such as 

 organic matter of vegetable or animal origin, mineral matter derived from dust 

 stirred up by the wind, chlorine from sea -spray, and ammonia from decaying 

 vegetable matter, or possibly other sources, can hardly be regarded as abnormal 

 impurities. At any rate, in the present connection the impurities which we 

 shall devote most attention to are those which are of artificial origin. 



By far the largest proportion of such are derived from incomplete combustion 

 of fuel, although there are other sources, such as road dust, fumes from chemical 

 factories, and the like, which contribute their quota. 



For the purpose of comparison it will be best to take the air of some country 

 station far removed from sources of pollution as representing what we may- 

 regard as practically pure air. Although doubtless there are other places which 

 would fulfil the necessary conditions, the only one at which observations are 

 being taken is Malvern Wells, and it will be seen from the figures in this paper 

 what a difference there is between the purity of the air there and in most of 

 our cities. 



Work of the Committee. 



It is impossible to devote more time to the general aspects of the question, 

 so I propose to describe in this paper the work of the Advisory Committee on 

 Atmospheric Pollution, and tn bring out some of the results obtained during the 

 last five years of its operations. 



This Committee was formed in 1912, and has published four Annual Reports, 

 commencing in 1914, the fifth Report being now at the printers. To avoid 

 misunderstanding it must be stated clearly that the function of this Committee 

 has been to investigate and measure only, with a view to providing accurate 

 data on the question of degree of pollution ; it has been no part of the Com- 

 mittee's work to consider methods of prevention. The Committee is now work- 

 ing under a grant from the Department of Scientific and Industrial Research, 

 and the method adopted is briefly as follows : — 



The work of devising methods of investigation and of co-ordinating inquiry, 

 as well as compiling and reporting upon resulte, has been the duty of the 



