ATMOSPHERIC DUST. 347 



the incandescent dust of aerolites. Baron Reichenbach collected on 

 the summit of Lahisberg a black ferruginous dust containing traces of 

 nickel and cobalt, which incontestably indicated its cosmic origin. Mr. 

 Nordenskjold collected a similar dust from off the snow of the polar 

 regions. 



For several years I have paid attention to the study of atmos- 

 pheric dust, and believe that I have proved that more or less con- 

 siderable quantities of dust derived from cosmic bodies are constantly 

 present in the air. The greater part of my experiments have been 

 performed in the meteorological observatory of Sainte-Marie-du-Mont, 

 Manche, where M. Herve-Mangon has placed the resources of his 

 establishment and laboratory at my disposition. I have endeavored 

 to collect large quantities of dust, so that I might carry on micro- 

 scopic and chemical analyses with precision. For this purpose I 

 used a surface of paper of two square metres, which I exposed hori- 

 zontally to the air ; I collected from it the dust which fell from the 

 air, sweeping it up with a small brush. I called this apparatus a dust- 

 table. The weight of the dust collected upon this surface at Sainte- 

 Marie-du-Mont varied from two to nine milligrammes (.03 to .14 

 grains troy) in twenty-four hours. The particles shown in Fig. 1 rep- 

 resent minute grains of magnetic oxide of iron, which were drawn out 

 from the dust by the magnet. They are greatly magnified, their real 

 diameter being only -fa of a millimetre ( T oVo ^ an inch). 



If we evaporate considerable volumes of rain-water, we shall obtain 

 a sediment which represents the air-dust ; if, then, we draw a magnet 

 through this sediment, we shall nearly always find little globules of 

 magnetic oxide of iron in it. Fig. 2 represents some of these glob- 

 ules, which I extracted from one hundred quarts of rain-water at 

 Sainte-Marie-du-Mont. 



We can distinguish several of these grains which have the form of 

 spherules, or granules that have undergone fusion. The sediment from 

 rain-water collected in Paris at the School of Bridges and Highways 

 at the Trocadero and the dust collected in one of the towers of Notre 

 Dame gave identical results (Fig. 3). 







Fig. 3. Corpuscles extracted by a Magnet from the Dust brought in bt the Wind in 

 a Tower op Notre Dame which is closed to Visitors. (500 Diameters.) 



These facts prove conclusively that the air holds in suspension mi- 

 nute microscopic particles of oxide of iron, some of which assume the 

 form of well-defined spherules. 



Similar spherules may be found everywhere in the dust of the air 

 and in rain-water and snow-water. I have found them in the sedi- 



