26 DILST. 



Eminent as are the services of dust in thedift'usion of light, 

 they aie no less important as the only means of diffusion or 

 distribution of rain and all that this involves for a habitable 

 world. 



It is known that water in the form of vapor requires to come 

 in contact with a body as a medium of condensation, when it 

 reaches the necessary coolness. In the cooler upper region of 

 the atmospheie water vapor seeks and finds such medium in the 

 ever present dust. The particles become the primary nuclei of 

 minute water globules of small specific gravity that float in 

 masses in the form of clouds carried hither and thither by air 

 currents. Condensation being initiated, the process goes on until 

 final precipitation takes place in the form of showers of rain with 

 all its attendant blessings. Without the nuclei which the dust 

 particles afford for the purpose, the atmosphere would he in a 

 constant state of excessive saturation, and the surface of the 

 earth the only condensing medium ; so it is easy to imagine 

 what the disastrous consequences would involve. There would 

 be no fog, no clouds, no rain, no showers, no snow, but copious 

 dew'S. There would simply be an extremely saturated atmos- 

 phere, seeking, when cooling began, something to wet or ice over. 

 Vegetation, the walls of our houses, ourselves, everything, acting 

 as media of condensation, would be dripping spectacles in 

 summer and clad in sheets of ice in winter. The now indispen- 

 sabl*^ umbrella would aft'ord no protection. Our houses might 

 be roofless so far as any shelter they could give from the soak- 

 ing atmosphere, and it is doubtful whether fire could be dis- 

 covered and continued under such physical conditions. It is 

 difficult to conceive the type of animal and vegetable life that 

 could exist in an environment so uninviting. Perhai)sfish, water- 

 lilies, and Kingsley's water babies may give us some clue. In 

 mountain regions the effects of a pure atmosphere as regards dust 

 would be more disastrous still. Their greater attracting in- 

 fluence as condensing media for the semi-liquid atmosphere 

 would create devastating deluges of water compared with which 

 tropical rains would seem April showers. The mountain sides 

 would be swept of all vegetation and soil into the valleys and 

 thence by tremendous floods and inundations to the sea, and 

 these forever recurring. The present slow, almost insensible. 



