554 



Mr. Horace T. Brown 



[March 22, 



Table I. — Diffusion of Atmospheric C0 2 through Single 

 Apertures of Varying Size. 



This of course implies, that as we make the aperture smaller, the 

 flow through a given unit of its area is proportionally increased — in 

 other words, the acceleration of flow is inversely proportional to the 

 diameters of the apertures. 



This unexpected fact, which lies at the root of the whole question 

 we are considering to-night, may be experimentally illustrated in a 

 variety of ways. 



We may, for instance, cause the aqueous vapour of the air to 

 diffuse into a similar series of flasks, using in this case strong 

 sulphuric acid as the absorbent, and determining the amount of dif- 

 fusion of the water vapour, by weighing the flasks from time to 

 time. You will see from the results of such an experiment that the 

 diffusion rates again follow pretty closely the ratios of the diameters 

 of the apertures, and are widely divergent from the ratios of areas. 

 (See Table II.) 



Table II. — Diffusion of Aqueous Vapour through Apertures 

 of Varying Size. 



This " diameter law " is also applicable to circular liquid surfaces, 

 the amount of absorption or evaporation from such surfaces varying, 

 under certain conditions, not in accordance with the areas of those 

 surfaces as might have been expected, but with their diameters. 



