THE MICROBIOLOGY OF THE ATMOSPHERE 



but corresponds with Sutton's formula for o-, where C = 0-64 (metre)*, 

 and m = 1-76. Sutton's work was apparently unknown to Stepanov when 

 these experiments were done, and so the data could not at the time be 

 analysed in terms of eddy diffusion. However, the agreement between 

 experiment and theory provides evidence that spore dispersal in air is 

 mainly controlled by eddy diffusion of the t^'pe postulated by Sutton 

 {see Table VII). The values for C and m obtained from Stepanov's 

 experiments agree well with those found in spore dispersal tests by other 

 workers (Table VIII), and with comparable data obtained by Richardson 

 (1920) for dispersal of smoke from a point source over distances of tens 

 of metres, where C = o-6 (metre)«, and m == 1-75. 



TABLE VII 



CALCULATION OF PARAMETERS FOR SUTTON's DIFFUSION EQUATION FROM 



stepanov's data (1935) 



Expt. 



E. E. Wilson & Baker (1946) liberated Lycopodimn spores at 7-5 ft. 

 above ground-level and caught them, not on glass slides on the ground as 

 Stepanov had done but, because they were interested in diseases of fruit 

 trees, on vertical sticky slides placed on three vertical posts at 1-5, 3-0, 

 and 5-1 metres down-wind from the source, and at thirteen heights above 

 ground at each distance; seven tests were done at wind speeds ranging from 

 17 to 7-2 metres per sec. Other tests measured the horizontal dispersion. 

 Wilson & Baker calculated the standard deviation of the spores deposited 

 at each distance in each test, and from their values for a we can now esti- 

 mate the parameters for Sutton's equation. In a few individual experi- 

 ments their values obtained for m lay outside the limits of 1-24 and 2-0 

 postulated by Sutton. But their mean value is m = 1-74 — thus agreeing 

 well with Sutton's theory {m = 1-75) and with Stepanov's experimental 

 value (;;/ = 1-76). Though their values for C^ agree well with Sutton's 

 findings, those for Cy are much higher, but agree with those of Gregory, 

 Longhurst & Sreeramulu (unpublished). 



54 



