FIGURES IN TEXT 



PAGE 



1. Pasteur's gun-cotton filter for airborne microbes ... 5 



2. Cunningham's aeroconiscope ....... 8 



3. Diagrammatic representation of layers of the atmosphere with a 



logarithmic vertical scale ....... 23 



4. Splash from impact of water drop (5 mm. diameter) falling with 



velocity of 440 cm. per sec. on a thin film of water ... 36 



5. Anthesis of false oat-grass {Arrhenatherum elatius): (i) closed 



anther; (2) open anther; (3) spikelets on a calm day; and (4) 

 spikelets in a wind ........ 41 



6. Diffusion of spore-cloud during horizontal travel in wind . . 48 



7. Test of agreement of W. Schmidt's and Sutton's diffusion theories 



with experiments using Lycopodium spores liberated over grass 

 field at Imperial College Field Station, Ascot, Berks.: {a) graph of 

 log CT against log x; (/;) graph of log o against log t . . -57 



8. Diagram showing relation between concentration x = no. of spores 



per unit volume; wind-speed = u. ; area dose, A.D. = no. of 

 spores passing through frame of unit area; and trap dose, 

 T.D. = no. of spores deposited on unit area of surface . . 58 



9. Streamlines of air and particle trajectories around a cylindrical 



obstruction ......... 59 



10. Observed relation between E per cent and k = Vsu/idg. Solid 



lines from Gregory & Stedman (1953). Broken lines = values 

 predicted by Langmuir & Blodgett (1949) for spheres, strips, 

 and cylinders for ^ = 10^ . . . . . . .60 



11. Diagram showing small wind-tunnel used in deposition study at 



Rothamsted Experimental Station, elevation view . . .61 



12. Diagram illustrating gravity theory of particle deposition . . 65 



13. Efficiency of deposition oi Lycopodium spores on zones across glass 



microscope slide at presentation angles from 0° to 90° as observed 



in wind-tunnel experiments ....... 66-67 



14. Mean efficiency of deposition o^ Lycopodium spores on glass micro- 



scope slide (all zones) at presentation angles of 0° to 180° . . 70 



15. Number of raindrops of various diameters passing per second 



through I sq. metre (horizontal), with rainfall of intensities varying 

 from 05 to 25 mm. per hr. . . . . . . .86 



16. Collection efficiencies of spores of diameters 4 to 40 /x by raindrops 



of diameters 003 to 50 mm. ...... 87 



17. Diagram of the Hirst automatic volumetric suction-trap: (i) eleva- 



tion facing wind; (2) plan of section through orifice; (3) elevation 



in side view ......... 100 



18. Diagram of six-stage Andersen sampler . . . . .102 



xi 



