THE MICROBIOLOGY OF THE ATMOSPHERE 



Fig. 13 shows that at 0° this edge drift fell behind the trailing edge, but 

 that when the shde was inclined at 15° or 30° to the wind, the edge drift 

 impacted on the slide. This is shown by the deposit on the leading edge 

 which greatly exceeded the expected value over the range 15° to 60°, 

 1-7 to 9-5 metres per sec. 



(iii) Mixed ejfects. Over most of the range of zones, presentation angles 

 and wind-speeds, the deposition was from a mixture of two or more 

 mechanisms whose relative importance can be roughly assessed from the 

 empirical results shown in Fig. 13. 



90'-' 

 Presentation angle 



135° '\l-1m./sec. 



Fig. 14.— Mean efficiency of deposition of Lycopodium spores on glass microscope 

 slide (all zones) at presentation angles of o° to i8o°. E = efficiency as percentage area dose 

 (Gregory & Stedman, 1953). Reproduced by permission from Annals of Applied Biology. 



MEAN DEPOSIT ON INCLINED SLIDES 



In the foregoing paragraphs, efficiencies of various arrangements of 

 a microscope slide, acting under different conditions as a spore trap, have 

 been measured and interpreted in terms of different deposition mechan- 

 isms acting on different surface zones of the slide. In practice, when 

 scanning a slide (or Petri dish trap), we usually need a mean value of 

 efficiency for the whole sampling area. Mean efficiencies for a microscope 

 slide with its long axis parallel to the y-axis, orientated at different presen- 

 tation angles to the x, y-plane (i.e. g+, or g_), are given in Fig. 14. They 

 are taken from the same results as were used in the preceding figure. Each 

 point of Fig. 14 represents values obtained in from one to eight experi- 

 ments. 



70 



