MM 



know LEDGE. 



April, 1915. 



that do fermentation took place in his dust-freed air, 

 knowing thai fermentation was caused by germs, 

 he arrived at the conclusion that there was some 



connection between dust and germs. Nowadays 

 we know that what is usually called dusl is really 

 multitudes of microbes adherin to genuine dust. 

 It was to Pasteur's credit thai the " genu theory" 

 of disease was discovered, and with the intro- 

 duction of Listerism it has hern asserted that 

 " more human lives have been saved than the 

 wars of the last century have sacrificed." The core 

 of Listerism is the use of the carbolic spray with 

 which a wound and the neighbouring air are dosed, 

 thus killing any fatal microbes. Now microbes 

 cannot live in fresh air and sunlight, and thus 

 doctors advocate a combination of these two as a 

 preventive. Again, the number of microbes varies 

 directly as the number of dust particles ; the 

 smaller the amount of dust the less the number of 

 mil robes, and consequently the decrease in pulmo- 

 nary diseases. What a hotbed of disease must our 

 dustbins be where organic refuse and coal ashes are 

 thrown to decompose together ! As has been stated 

 previously, the higher we ascend the smaller the 

 number of dust particles, and consequently we see 

 why mountain air is so beneficial to persons suffer- 

 ing from consumption. 



Physiographical Aspect. 

 Represented as a short genealogical tree : — 

 Atmospheric Dust. 



Mineral Volcanic Products of Cosmic or 



(Salts) (various) Combustion Meteoric 



(carbon, sulphur) (chiefly iron) 



Dr. J. Aitken was the first to show that when 

 water vapour condenses in the atmosphere it always 

 does so on some nucleus, e.g., dust particles. His 

 dust counter employs this principle. These are 

 not, however, the only agency. Mr. C. T. R. Wilson 

 has shown that air which is free from dust, but 

 ionised, is capable of having water vapour condensed 

 in it. Very probably phenomena such as fogs, 

 clouds, mist, or rain are due to both these influences, 

 dust being plentiful and ionisation caused by the 

 radio-active elements present in the atmosphere, 

 and by sunlight. More recently Dr. Aitken has 

 offered an explanation of fog. If sulphur dioxide 

 be exposed to a strong beam of white light it decom- 

 poses, slowly producing a yellow fog of sulphur. 

 Now sulphur dioxide issues forth with other 

 products of combustion from the mouths of 

 chimneys. With the action of sunlight, and a 

 little moisture in the form of water vapour being 

 present, a fog is produced. The characteristics of 

 the London fog are easily explained by this. 



The magnificent sunsets which can be seen in 

 different parts of the Earth, and the reddish colour 

 at both dawn and twilight, are due directly to the 

 presence of dust particles and water vapour. In 

 the morning and evening the light from the Sun 



has to travel through the greatest thickness of air 

 and dust, and since the blue rays are more easily 

 scattered than the red we have the familiar 

 gradation of spectral tints seen at these times. 

 Occasionally there is a second sunset, which is 

 a reflection in the clouds of a more brilliant primary 

 one. These primary and reflected sunsets were 

 much in evidence whilst the Krakatoadust (autumn, 

 1883) was spread in a layer about fifteen miles 

 above the surface of the Earth in a broad belt 

 about the Tropics, lasting an hour or two after the 

 real sunset. The " Bishop's Ring " was the name 

 given to the coronae which were formed by the Sun 

 shining through the dust. These coronae were an 

 outer edging to the Sun's disc, blue on the inside, 

 passing through the various colours of the spectrum, 

 the outermost being red. The sunsets at that time 

 were unusually vivid, and the story runs of an 

 American fire brigade setting out to put out an 

 alleged fire at a neighbouring village from which 

 the glow appeared to come. But the Krakatoa 

 eruption is not the only instance. After the Messina 

 disturbance a few years ago the sunsets attracted 

 people's attention, and it was noticed in meteoro- 

 logical circles that our climatal conditions suffered 

 a change. In 1783 volcanic dust (traced afterwards 

 from Skaptar Jokul, Iceland) descended on the 

 Orkneys and Shetlands and North Scotland, 

 ruining crops. In this way the dust was carried 

 a distance of over six hundred miles. Coseguina 

 (Nicaragua), a volcano, in 1835 threw out enough 

 dust to cause utter darkness for thirty-five miles 

 radius, and which, when it fell, was ten feet deep. 

 In four days an upper aerial current carried some 

 dust seven hundred miles. So-called " mud lavas " 

 are really the extremely fine volcanic dusts gathered 

 and mixed by the water, belching forth out of the 

 crater, and often doing more damage than a true 

 lava stream. 



Cosmic dust is formed by the disintegration of 

 meteorites owing to friction (they travel from 

 twenty-five to forty miles per second) with our 

 atmosphere. The luminosity of shooting stars is 

 due to the rapid combustion of the meteoric dust 

 in the train of a meteorite. 



The presence of sodium salts in the air is easily 

 demonstrated by brushing the dust from one's 

 clothes into a non-luminous flame. The character- 

 istic yellow of sodium is much in evidence. Very 

 probably the ocean spray accounts for its presence. 

 Salts of copper have been detected in city air, 

 and accounted for by the electric flashes of overhead 

 cables. 



With the chemical we arrive at the most interest- 

 ing, and perhaps the most important, side of dust 

 phenomena. Until recently it was considered that 

 fire-damp was the sole cause of coal-mine explosions, 

 but experience has shown that within the last ten 

 years explosions have occurred more frequently in 

 well-ventilated mines. Thus causes have been traced 

 to coal dust which, in the presence of air, is very 

 explosive. Probably the reason is that oxygen 



