METALS IN THK ATMOSI'II KKK. 247 



i)h:Uo. ()!• soda sulj)lia((>, which shows llial thoso subslanccs, allliou<^-h 

 elHorscviit, arc oiil\ accidciilal in the aliuos[)hci-c. The sanu' is tnieof 

 nitrate of lime and calcium chloride, which are readily <iiven up to 

 the air, although their sources are not to he found in the atmosphere. 



Accldchtdl substances. — Besides the dusts which the normal air 

 almost always contains, there are those more exceptional ones of 

 volcanic oriirin. Such was a dust wdiich fell with the snow^ in Nor- 

 way on .March -Ji)-:')!), ISTS; it was <>-|-ay an<l Hhrous. formed of grains 

 of ().()"2 to ().().') nun. diameter. These were characteristic fragments of 

 jiuniice aiul little grains of iron oxide in octahedron cuboids. There 

 are numerous examples of the transportation for great distances of 

 dusts, volcanic cinders, and ashes from great fires. For instance, 

 the sand that fell on the western Canaries on the Tth of February, 

 ISt;;), came in all pr()l)ai)ility from the Sahara, more than 200 miles. 

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

 Azores some forty days aftei- the begiiniing of the catastrophe. The 

 celebrated dry fog, which in 1TS8 covered all Furope for three months, 

 first appeared at Copenhagen, where it continued one hundred and 

 twenty-six days. Tt was caused by an eruption in T(;eland. In Se]}- 

 teniber, lS4r), a phenomenon of the same soi-t but less formidable was 

 observed on the Shetland and Orkney Islands. This came from an 

 eruption of Ilecla on Sej)tember 2, and the cinders had traveled more 

 than .■">()() miles. The atoms that fell during the cyclone of 187!) in the 

 vicinity of Naples and Palermo Avere tinged with yellow. In that 

 region also have been found black sj)heres and globules, susceptible to 

 the magnet, the diameters of which at Palei'ino were between 0.004 

 and 0.02S nun.: at Nai)les 0.007 to 0.020 nun., and from 0.011 to 0.040 

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

 sphei'ules following on the coasts of Algeria and Tunis. 



A shower of cinders fell in the vicinity of Ftna from the 24lh to 

 the 2i>th of May, ISSt;; examined in the observatory of Palermo, they 

 showed the little laminated crystals characteristic of the ejections of 

 Ktna. Similar ])henomenon ha\'e been ()l)sei"ved after the eruption 

 of Krakalao. 



Conclusion. — Leaving aside the dusts which are teini)orarily 

 brought into the atmosi)here by volcanic eru])ti()ns or other accidents, 

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

 sodium, calcium, magnesimn.. aluminum, and more esj)ecia]l\' nickel, 

 cobalt, and iron. These hav(> all a teri'estrial origin, e.\cej)t the last 

 three, which come from out of planetary space. The proportion of 

 solid matter in the air does not appear great enough to be of sig- 

 nificance in the i)hysi()grai)hy of the earth, but almost a third of it 

 is c()m[)osed of organic matter containing living germs. This part 

 at least concerns the biologist and assumes some im})ortanc<' from its 

 pathological conse<|uences. 



