I 



CORRESPONDING SOCIETIES. 37 



Mr. Symons i-emarked that Mr. Darwin had undertaken to gi\e all 

 the necessary information, and so had Mr. Davison. 



In answer to a question from Mr. Mills, he added that it was not 

 essential that an instrument should be placed in a mining district, but it 

 was desirable that they should be scattered throughout the country. 



Mr. Seward said that he would try to get one placed in one of the 

 deep mines of South Wales. 



The Chairman hoped that by next year some of the Corresponding 

 Societies would have something to report on this question. Mr. Darwin 

 had kindly offered to explain, after the termination of the Conference, 

 the mechanical details to any persons interested. 



Section B. 



Pollution of Air in Totvns. — Dr. G. H. Bailey said that for three or 

 four years they had been engaged in Manchester, in connection with the 

 Manchester Field Naturalists, in examining the air of towns with the 

 view of ascertaining the extent to which it was polluted. This was a 

 question of much practical importance, for the amount of the pollution was 

 a pretty good indication of the death rate. Those times of the year at 

 which the air was most polluted were those at which the death-rate was 

 highest. Hitherto there had been very little attempt to ascertain the 

 nature and degree of the pollution, and it had been their endeavour to 

 examine the methods by which the pollution of town air could be detected, 

 and to determine its nature and amount. They had almost perfected a 

 method for determining the amount of sulphur compounds in the air, and 

 one for measuring the amount of sunlight in towns. They had found that, 

 whilst in extreme cases of pollution carbonic acid gas varied between four 

 and seven parts in 10,000, the sulphur compounds varied from less than 

 one up to fifty per million parts. The pollution varied practically as did 

 the amount of the sulphur compounds. The work was hardly yet in so 

 complete a state that he could recommend its adoption at a large number 

 of other towns, but it would interest the delegates to know what had been 

 done. They wei'e at that time working at a method for determining the 

 nature and amount of the pollution of different districts of large towns. 

 The work already done had been chronicled in the ' Journal of the 

 Manchester Field Naturalists' for 1893. They had come to the conclusion 

 that about 50 per cent, of the daylight was cut off by the smoke of a town, 

 speaking of that form of light which could be registered, viz., the actinic 

 rays. They had found that the centres of large towns sometimes showed 

 a diminution, as compared with the suburbs, of about 50 per cent., the 

 diminution of light in the centres of large towns as compared with the- 

 ■open country amounting to about 75 per cent. When their methods 

 were more fully perfected they hoped to have the co-operation of membei-s 

 in more rural districts. They had been working at the indoor as well as 

 the outdoor pollution of the air. 



Mr. Slater remarked that the plants of very smoky districts were 

 either destroyed or injuriously affected by the smoke. 



The Chaii'man said that it was well known to London naturalists that 

 lichens were once common on tree trunks in Epping Forest, but few 

 if any were to be found there now. It is too near London for them to 

 flourish, 



Mr. Symons remarked that Dr. Bailey had apparently employed the 



