206 THE AMERICAN MONTHLY [July, 



is a dense volume of Carbonaceous matter projected into the 

 atmosphere, at various altitudes; that from the smoke-stack of 

 the locomotive being least in height, but ejected with greatest 

 expulsive force, as cinder and smoke ; while that from high 

 chhnneys attached to manufacturing plants is delivered at an 

 altitude of one hundred feet or more. These two conditions 

 prevail at the point where I secured the specimens of material 

 with Avhich to eluci'hite the matter. I have occasion toexpose 

 daily, for the blue-copying process, a large polished plate of 

 glass having an area of fifteen square feet of surface, and I ob- 

 served that the surface every few days became covered with a 

 coating of carbonaceous dust. It then occurred to me to collect 

 this dust by brushing the entire surface with a soft roll of cloth. 

 Gathering the residuum together and submitting it to micros- 

 copic inspection ; I found the minute spherules, as described 

 and illustrated in the Journal. These were of varied charac- 

 ters, some very black and opaque, others transparent or opal- 

 escent and often filled with mmute air-bubbles. Apart from 

 the spherules, there was a variety of other mineral substances 

 small crystals of calcite, small circular plates resembling dia- 

 toms of the cydotella species, various transparent plant fibres, 

 etc. This dust represented the finest particles that were trans- 

 ported in the atmosphere and would take the longest time to 

 settle down. 



This particular collection of dust particles did not fully set- 

 tle the source of the dust ; bul as I observed a boy sweeping off 

 the roofs or some box cars in ihe car- repair yar Is, I got him to 

 hand me down a packet of the cinder dust. I sifted it through 

 muslin and examined it under the Microscope, when I found 

 it to be composed of myriads of the opaque, transparent, and 

 o})alescent sperules of the kind found in the dust brushed from 

 the glass plate. On applying a strong horse-shoe magnet to the 

 dust, the material was found to bestrongly magnetic, thousands 

 of the black, opaque spherules clinging to the magnetic poles. 

 In the material derived from the roof of the car, the spherules 

 range in size from one-fiftieth of an inch, to the most minute 

 in size. In order that the editor of the Journal, may, if deemed 

 desirable, verify my statement, I have forwarded two packets 

 of the material, one from the roof of a car, the other composed 

 of brushings from the French plate glass. 



