METALH IN THE ATMOSPHERE. 247 



phatc. or soda siilphato, which shows thai tht^sc suhstancos, although 

 eiiiorscent, ai'c only accick'ntal in the atniospluM-c. The same is true of 

 nitrate of iinie and cnk-iuni chloride, which are readily i>Mveii up to 

 the air, although tlu'ir soiu'ces are not to he found in th(> atniospliere. 



Accidentid suhfitaiu-cs. — Besides the dusts which the noruud air 

 almost always contains, there are those more exceptional ones of 

 \()lcanic origin. Such was a dust which fell with the snow in Nor- 

 way on IMarcli 21)-80, 18TS; it was gray and fibrous, formed of grains 

 of OAYl to O.Oo nun. diameter. These were characteristic fragments of 

 pumict' and little gi'ains of iron oxide in octahedron cuboids. There 

 are niuneroiis examples of the transportation for great distances of 

 (lusts, volcanic cinders, and ashes from great fires.' For instance, 

 the sand that fell on the western Canaries on the Ttli of Fel)ruary, 

 ISC):^, came in all prol)al)ility from the Sahara, more than 200 miles. 

 More recently the cinders from the great Chicago fire arrived at the 

 Azores some forty days after the beginning of the catastrophe. The 

 celebrated dry fog, which in 17S;> covered all P^urope for three months, 

 first aj)peared at Copenhagen, where it continued one hundred and 

 twenty-six days. It was caused l)y an eru])ti()n in Iceland. In Sep- 

 tember, 1845, a phenomenon of the same sort but less formidable was 

 <)bser\'ed on the Shetland and Orkney Islands. This came from an 

 eruption of Ilecla on September 2, and the cinders had traveled more 

 than 500 miles. Tlie atoms that fell during the cyclone of 1879 in the 

 vicinity of Naples and ralermo were tinged with yellow. In that 

 region also have been found black spheres and globules, susceptible to 

 the magnet, the diameters of which at Palernu) were between 0.004 

 aiul 0.0-ji8 nun.; at Naples 0.007 to 0.020 nun., and from 0.011 to 0.040 

 mm. at Teramo. These measurements agree well with those magnetic 

 spherules following on the coasts of Algeria and Tunis. 



A shower of cinders fell in the vicinity of Etna from the 24tli to 

 the --iUth of May, 188(); examini'd in the obser\'atory of Palermo, they 

 showed the little laminated crystals characteristic of the ejections of 

 Ktna. Similar phenomenon have been observed after the erui)tion 

 of Krakatao. 



Coitcl iisio)). — Leaving aside the dusts which are temporarily 

 bi-oiight into the atmosi)here by volcanic erui)tions or other accidents, 

 we see that the air ordinarily contains only a small number of metals — 

 sodium, calcium, magnesium, aluminum, and more es})ecially nickel, 

 cobalt, and iron. These ha\'e all a tei'restrial oi-igin, excei)t the last 

 three, which come from out of planetary space. The j)rop()rtion of 

 solid matter in the air does not ai)pear great enough to be of sig- 

 nificance in the physiogi-aphy of the earth, but almost a third of it 

 is comi)()sed of organic matter containing living gei'uis. This part 

 at least concerns the biologist and assumes some imj)or(ance from its 

 pathological consequences. 



