518 



Dr. P. F. Frankland. 



[June 10, 



These figures show that in cold weather, especially when the 

 ground is covered with snow, the number of organisms in the air is 

 very much reduced and presents a very striking contrast to the 

 number found in the warmer weather, even immediately after much 

 rain. 



The experiments made on the 9th of March show that during cold 

 and dry weather with a strong east wind blowing over London, a 

 large number of micro-organisms may still be present in the air ; for 

 although the tube-experiment made on that day cannot be regarded 

 as satisfactory, yet from the number falling on the square foot it is 

 evident that they must have been very abundant, certainly very much 

 more abundant than on the 16th of March, when with much the same 

 temperature the wind was more moderate and blowing from the 

 north-west. 



It is particularly noticeable that even after such exceedingly heavy 

 rain as was experienced on the morning of the 22nd of May, within a 

 few hours afterwards the number of micro-organisms in the air should 

 be as abundant as usual. 



It will be seen on comparing the number in the above table that, 

 with the exception of the experiment made on January 21st, when 

 snow was on the ground and actually falling at the time, the number 

 of micro-organisms present in the air collected on the roof of the 

 Science Schools, never fell so low as in some of the experiments to be 

 presently mentioned, which were made in the country. 



Taking the average of the experiments recorded above, it will be 

 seen that the mean number of organisms found in 10 litres of air 

 amounted to 35, whilst an average of 279 fell on 1 square foot in 

 one minute. 



